View source for Mekong

{{short description|Major river in Southeast Asia}}
{{Other uses}}
{{Use dmy dates|date=March 2021}}
{{Infobox river
| name               = Mekong River
| name_other         = {{lang|zh-Hans|
湄公河}} (Méigōng Hé) / {{lang|zh-Hans|澜沧江}} (Láncāng Jiāng)<br>{{lang|my|မဲခေါင်မြစ်}} (Megaung Myit)<br>{{lang|lo|ແມ່ນ້ຳຂອງ}} (Maenam Khong)<br>{{lang|th|แม่น้ำโขง}} (Maenam Khong)<br>{{lang|km|ទន្លេមេគង្គ}} (Tônlé Mékôngk)<br>{{lang|vi|Sông Mê Kông}} / {{lang|vi|Sông Cửu Long}} ({{Vi-nom|九龍}})
| name_etymology     = 
| image              = Mekong-River-Near-Luang-Prabang.jpg
| image_size         = 300px
| image_caption      = Mekong River, [[Luang Prabang]], Laos
| map                = Mekong river basin.png
| map_size           = 300px
| map_caption        = Mekong River watershed
| pushpin_map        = 
| pushpin_map_size   = 300px
| pushpin_map_caption= 
| subdivision_type1  = Country
| subdivision_name1  = [[China]], [[Myanmar]], [[Laos]], [[Thailand]], [[Cambodia]], [[Vietnam]]
| subdivision_type2  = 
| subdivision_name2  = 
| subdivision_type3  = 
| subdivision_name3  = 
| subdivision_type4  = 
| subdivision_name4  = 
| subdivision_type5  = 
| subdivision_name5  =

| length             = {{cvt|4350|km|mi}} 
| width_min          = 
| width_avg          = 
| width_max          = 
| depth_min          = 
| depth_avg          = 
| depth_max          = 
| discharge1_location= [[Mekong Delta]], [[South China Sea]]
| discharge1_min     = {{cvt|1,400|m3/s|cuft/s}}
| discharge1_avg     = {{cvt|16,000|m3/s|cuft/s}}
| discharge1_max     = {{cvt|39,000|m3/s|cuft/s}}
| source1            = Lasaigongma ({{lang|zh-CN|拉赛贡玛}}) Spring
| source1_location   = Mt. Guozongmucha ({{lang|zh-CN|果宗木查}}), [[Zadoi County|Zadoi]], [[Yushu Tibetan Autonomous Prefecture]], [[Qinghai]],
| source1_coordinates= {{coord|33|42.5|N|94|41.7|E|type:river_region:CN-63|display=inline}}
| source1_elevation  = {{cvt|5224|m}}
| mouth              = [[Mekong Delta]]
| mouth_location     = [[Vietnam]]
| mouth_coordinates  = {{coord|10.19|106.75|display=it}}
| mouth_elevation    = {{cvt|0|m}}
| progression        = 
| river_system       = 
| basin_size         = {{cvt|795,000|km2|mi2}}
| tributaries_left   = [[Srepok River|Srepok]], [[Nam Khan (river)|Nam Khan]], [[Tha River|Tha]], [[Nam Ou]]
| tributaries_right  = [[Mun River|Mun]], [[Tonlé Sap]], [[Kok River|Kok]], [[Ruak River|Ruak]]
| custom_label       = Protection Status
| custom_data        = 
| extra              = {{Infobox mapframe |wikidata=yes |zoom=3 |height=250 | stroke-width=1.5 |coord {{WikidataCoord|display=i}}}}
}}
{{Contains special characters|Tibetan}}
{{Contains special characters|Lao}}
{{Contains special characters|Khmer}}
{{Contains special characters|Burmese}}

The '''Mekong''' or '''Mekong River''' is a [[trans-boundary river]] in [[East Asia]] and [[Southeast Asia]]. It is the world's [[List of rivers by length|twelfth-longest river]] and [[List of longest rivers of Asia|the third-longest]] in Asia<ref name="Liuetal2009">{{cite journal |author1=S. Liu |author2=P. Lu |author3=D. Liu |author4=P. Jin |author5=W. Wang |year=2009 |title=Pinpointing source and measuring the lengths of the principal rivers of the world |journal=International Journal of Digital Earth |volume=2 |issue=1 |pages=80–87 |doi=10.1080/17538940902746082 |url=https://zenodo.org/record/897056 |bibcode=2009IJDE....2...80L |s2cid=27548511}}</ref> with an estimated length of {{cvt|4909|km|mi|0}}<ref name="Liuetal2009" /> and a [[drainage area]] of {{cvt|795000|km2|sqmi|-3}}, discharging {{cvt|475|km3|cumi|0}} of water annually.<ref name ="MRC_2010a">{{cite web |website=Mekong River Commission |year=2010 |title=State of the Basin Report, 2010 |location=Vientiane |url=http://www.mrcmekong.org/assets/Publications/basin-reports/MRC-SOB-report-2010full-report.pdf}}</ref>
From its [[headwater]]s in the [[Tibetan Plateau]], the river runs through [[Southwest China]] (where it is officially called the '''Lancang River'''), [[Myanmar]], [[Laos]], [[Thailand]], [[Cambodia]], and [[southern Vietnam]]. The extreme seasonal variations in flow and the presence of [[Rapids|rapid]]s and [[waterfall]]s in the Mekong make [[navigation]] difficult. Even so, the river is a major trade route between Tibet and Southeast Asia. The construction of [[hydroelectric dam]]s along the Mekong in the 2000s through the 2020s has caused serious problems for the river's [[ecosystem]], including the exacerbation of [[drought]].<ref>{{cite news |last1=Sasipornkarn |first1=Emmy |title=A dam-building race threatens the Mekong River |url=https://www.dw.com/en/a-dam-building-race-threatens-the-mekong-river/a-50049206 |access-date=18 August 2019 |work=Deutsche Welle |date=16 August 2019}}</ref><ref>{{cite news |last1=Sripiachai |first1=Pattanapong |title=Mekong River falls to critical level, sand dunes emerge |url=https://www.bangkokpost.com/thailand/general/1782349/mekong-river-falls-to-critical-level-sand-dunes-emerge |access-date=26 November 2019 |work=Bangkok Post |date=29 October 2019}}</ref><ref>{{Cite news |last=Beech |first=Hannah |url=https://www.nytimes.com/2020/04/13/world/asia/china-mekong-drought.html |title=China Limited the Mekong's Flow. Other Countries Suffered a Drought. |date=13 April 2020 |work=The New York Times |access-date=14 April 2020 |language=en-US |issn=0362-4331}}</ref>

==Names==
The Mekong was originally called ''Mae Nam Khong'' from a contracted form of [[Tai language|Tai]] shortened to ''Mae Khong''.<ref name=ntd>{{citation |last=Nguyen |first=Thi Dieu |author-mask=Nguyen Thi Dieu |page=[https://books.google.com/books?id=RXbFclX4YcwC&pg=PA36 36] |url=https://books.google.com/books?id=RXbFclX4YcwC |title=The Mekong River and the Struggle for Indochina: Water, War, and Peace |location=Westport |publisher=Praeger |date=1999 |isbn=9780275961374}}</ref> In Thai and Lao, ''Mae Nam'' ("Mother of Water[s]") is used for large rivers and ''Khong'' is the proper name referred to as "River Khong". However, ''Khong'' is an archaic word meaning "river", loaned from [[Austroasiatic languages]], such as Vietnamese ''sông'' (from *''krong'') and Mon ''kruŋ'' "river", which led to [[Chinese language|Chinese]] {{lang|zh|{{linktext|江}}}} whose [[Old Chinese]] pronunciation has been [[linguistic reconstruction|reconstructed]] as {{IPA|/*kˤroŋ/}}<ref>Baxter-Sagart.</ref> and which long served as the proper name of the [[Yangtze]] before becoming a generic word for major rivers. To the early European traders, the Mekong River was also known as ''Mekon River'', ''May-Kiang River'' and ''Cambodia River''.<ref>Reid, H. (1857). ''A System of Modern Geography ... with Exercises of examination. To which are added treatises on Astronomy and Physical Geography''. United Kingdom: (n.p.).</ref>
<ref>''Universal Gazetteer of the World: A Dictionary, Geographical, Historical and Statistical, of the Various Kingdoms, States, Provinces, Cities, Towns, Forts, Harbors, Rivers, Lakes, Seas, Mountains, &c., in the World ... Also the Census of 1850''. (1852). United States: Z. & B. F. Pratt.</ref><ref>''A Gazetteer of the World: Brazil–Derry''. (1856). United Kingdom: A. Fullarton.</ref>
<ref>Roberts, G. (1834). ''The Elements of Modern Geography and General History, on a Plan Entirely New ... New Edition ... Improved, Etc.'' United Kingdom: (n.p.).</ref><ref>Hamilton, W. (1815). ''The East India Gazetteer: Containing Particular Descriptions of the Empires, Kingdoms, Principalities, Provinces, Cities, Towns, Districts, Fortresses, Harbours, Rivers, Lakes, &c. of Hindostan, and the Adjacent Countries, India Beyond the Ganges, and the Eastern Archipelago; Together with Sketches of the Manners, Customs, Institutions, Agriculture, Commerce, Manufactures, Revenues, Population, Castes, Religion, History, &c. of Their Various Inhabitants''. United Kingdom: J. Murray.</ref>

The local names for the river include:
# From Tai:
#*{{langx|th|แม่น้ำโขง}}, {{IPA-th|mɛ̂ː náːm kʰǒːŋ|}}, or just {{lang|th|แม่โขง}} {{IPA-th|mɛ̂ː kʰǒːŋ|}}.
#*{{langx|nod|น้ำแม่โขง}}, {{IPA-nod|náːm mɛ̂ː kʰǒːŋ|}}, or just {{lang|nod|น้ำโขง}} {{IPA-nod|náːm kʰǒːŋ|}}.
#*{{langx|tts|แม่น้ำของ}}, {{IPA-lo|mɛ̄ː nâːm kʰɔ̌ːŋ|}}, or just {{lang|tts|แม่ของ}} {{IPA-lo|mɛ̄ː kʰɔ̌ːŋ|}}.
#*{{langx|lo|ແມ່ນ້ຳຂອງ}}, {{IPA-lo|mɛ̄ː nâːm kʰɔ̌ːŋ|}}, or just {{lang|lo|ນ້ຳຂອງ}} {{IPA-lo|nâːm kʰɔ̌ːŋ|}}.
#*[[Tai Lue language|Tai Lue]]: {{script|Talu|น้ำแม่ของ}} {{IPA-lo|nâːm mɛː kʰɔ̌ːŋ|}}, {{script|Talu|น้ำของ}} {{IPA-lo|nâːm kʰɔ̌ːŋ|}}.
#*{{langx|shn|ၼမ်ႉၶွင်}} {{IPA-shn|nâm.kʰɔ̌ŋ|}} or {{lang|shn|ၼမ်ႉမႄႈၶွင်}} {{IPA-shn|nâm.mɛ.kʰɔ̌ŋ|}}.
# Other:
#*{{langx|vi|Sông Mê Kông}} ({{IPA-vi|ʂə̄wŋm mē kə̄wŋm|IPA}}) or {{lang|vi|Sông Cửu Long}}, ({{vi-nom|九龍}} ''Nine Dragons River'' {{IPA-vi|ʂə̄wŋm kɨ̂w lāwŋm|}}).
#*Chinese: {{zh|labels=no|c=湄公河 |p=Méigōng hé}}.
#*{{langx|my|မဲခေါင်မြစ်}}, {{IPA-my|mɛ́ɡàʊɰ̃ mjɪ̰ʔ|IPA}}.
#*{{langx|km|ទន្លេធំ}} ''Tônlé Thum'' {{IPA-km|tɔnlei tʰum|}} (lit. "Big River" or "Great River") <!-- Note: UNGEGN romanization --> or {{lang|km|មេគង្គ}} ''Mékôngk'' {{IPA-km|meːkɔŋ|}}, {{lang|km|ទន្លេមេគង្គ}} ''Tônlé Mékôngk'' {{IPA-km|tɔnlei meikɔŋ|}}.
#*[[Khmuic]]: {{IPA|[ŏ̞m̥ kʰrɔːŋ̊]}}, '{{IPA|ŏ̞m̥}}' means 'river' or 'water', here it means 'river', '{{IPA|kʰrɔːŋ̊}}' means 'canal'. So '{{IPA|ŏ̞m̥ kʰrɔːŋ̊}}' means 'canal river'. In the ancient time Khmuic people called it '{{IPA|[ŏ̞m̥ kʰrɔːŋ̊ ɲă̞k̥]}}' or '{{IPA|[ŏ̞m̥ kʰrɔːŋ̊ ɟru̞ːʔ]}}' which means 'giant canal river' or 'deep canal river' respectively.

==Course==
The Mekong rises as the '''Za Qu''' ({{bo|t=རྫ་ཆུ་|w=rDza chu|z=Za qu}}; {{zh|c=扎曲 |p=Zā Qū}}) and soon becomes known as the '''Lancang River''' ({{zh|s=澜沧江 |t={{linktext|瀾滄|江}} |p=Láncāng Jiāng}}, from the old name of Lao kingdom [[Lan Xang]]; the characters may also be literally understood as "turbulent green river"). It originates in the "[[Sanjiangyuan|three rivers source area]]" on the [[Tibetan Plateau]] in the [[Sanjiangyuan National Nature Reserve]]. The reserve protects the headwaters of, from north to south, the [[Yellow River|Yellow]] (Huang He), the [[Yangtze]], and the Mekong Rivers.<ref name="MRC_2010a" /> It flows through the [[Tibetan Autonomous Region]] and then southeast into [[Yunnan]] Province, and then the [[Three Parallel Rivers of Yunnan Protected Areas|Three Parallel Rivers Area]] in the [[Hengduan Mountains]], along with the Yangtze to its east and the [[Salween River]] (Nu Jiang in Chinese) to its west.

Then the Mekong meets the China–Myanmar border and flows about {{cvt|10|km|mi|sigfig=1}} along that border until it reaches the [[tripoint]] of China, [[Myanmar]] and [[Laos]]. From there it flows southwest and forms the border of Myanmar and Laos for about {{cvt|100|km|mi|sigfig=1}} until it arrives at the tripoint of Myanmar, Laos, and [[Thailand]]. This is also the point of confluence between the [[Ruak River]] (which follows the Thai–Myanmar border) and the Mekong. The area of this tripoint is sometimes termed the [[Golden Triangle (Southeast Asia)|Golden Triangle]], although the term also refers to the much larger area of those three countries that was notorious as a drug producing region.

From the Golden Triangle tripoint, the Mekong turns southeast to briefly form the border of Laos with Thailand.

Khon Pi Long is a series of [[Rapids|rapid]]s along a {{cvt|1.6|km|mi|1}} section of the Mekong River dividing Chiang Rai and Bokeo Province in Laos. The name of the rapids means 'where the ghost lost its way'.<ref name="BP-20170115">{{cite news |last1=Wangkiat |first1=Paritta |title=Against the flow |url=https://www.bangkokpost.com/news/special-reports/1180397/against-the-flow |access-date=3 May 2018 |work=Bangkok Post |issue=Spectrum |date=15 January 2017}}</ref> It then turns east into the interior of Laos, flowing first east and then south for some {{cvt|400|km|mi}} before meeting the border with Thailand again. Once more, it defines the Laos-Thailand border for some {{cvt|850|km|mi}} as it flows first east, passing the capital of Laos, [[Vientiane]], then turns south. A second time, the river leaves the border and flows east into Laos soon passing the city of [[Pakse]]. Thereafter, it turns and runs more or less directly south, crossing into [[Cambodia]].

At [[Phnom Penh]] the river is joined on the right bank by the river and lake system the [[Tonlé Sap]]. When the Mekong is low, the Tonle Sap is a [[tributary]]: water flows from the lake and river into the Mekong. When the Mekong floods, the flow reverses: the floodwaters of the Mekong flow up the Tonle Sap.

Immediately after the Sap River joins the Mekong by Phnom Penh, the [[Bassac River]] branches off the right (west) bank. The Bassac River is the first and main distributary of the Mekong. This is the beginning of the Mekong Delta. The two rivers, the Bassac to the west and the Mekong to the east, enter Vietnam shortly after this. In Vietnam, the Bassac is called the Hậu River (Sông Hậu or Hậu Giang); the main, eastern, branch of the Mekong is called the [[Tiền River]] or Tiền Giang. In Vietnam, distributaries of the eastern (main, Mekong) branch include the [[Mỹ Tho River]], the [[Ba Lai River]], the [[Hàm Luông River]], and the [[Cổ Chiên River]].

==Drainage basin==
[[File:Chamdo Mekong.png|thumb|Mekong River south of [[Chamdo]].]]
[[File:Phou si - Mekong River - Luang Prabang Laos プーシーの丘、メコン川 ラオス・ルアンプラバーン DSCF6787.jpg|thumb|The Mekong from [[Phou si]]]]
[[File:Nam Ou River confluence in Mekong Laos.jpg|thumb|The confluence of the Mekong and the [[Nam Ou]] Rivers, [[Laos]]]]

The Mekong Basin is frequently divided into two parts: the "upper Mekong basin" comprising those parts of the basin in [[Tibet Autonomous Region|Tibet]], [[Yunnan]] and eastern [[Myanmar]], and the "lower Mekong basin" from [[Yunnan]] downstream from China to the [[South China Sea]].<ref name ="MRC_2005">{{cite web |author=Mekong River Commission |year=2005 |title=Overview of the Hydrology of the Mekong Basin |publisher=MRC, Vientiane, Laos |url=http://www.mekonginfo.org/assets/midocs/0001968-inland-waters-overview-of-the-hydrology-of-the-mekong-basin.pdf |author-link=Mekong River Commission |access-date=21 April 2012 |archive-date=13 July 2018 |archive-url=https://web.archive.org/web/20180713003412/http://www.mekonginfo.org/assets/midocs/0001968-inland-waters-overview-of-the-hydrology-of-the-mekong-basin.pdf |url-status=dead}}</ref> From the point where it rises to its mouth, the most precipitous drop in the Mekong occurs in the upper Mekong basin, a stretch of some {{cvt|2200|km|mi|}}. Here, it drops {{cvt|4500|m|ft||abbr=out}} before it enters the lower basin where the borders of Thailand, Laos, China, and Myanmar come together in the Golden Triangle. Downstream from the Golden Triangle, the river flows for a further {{cvt|2600|km|mi|}} through Laos, Thailand, and [[Cambodia]] before entering the [[South China Sea]] via a complex delta system in [[Vietnam]].<ref name="MRC_2005" />

===Upper basin===
The upper basin makes up 24% of the total area and contributes 15–20% of the water that flows into the Mekong River. The [[catchment]] here is steep and narrow with [[Soil erosion]] being a major problem and as a result of this, approximately 50% of the sediment in the river comes from the upper basin.

In Yunnan Province in China, the river and its tributaries are confined by narrow, deep gorges. The tributary river systems in this part of the basin are small. Only 14 have catchment areas that exceed {{cvt|1000|km2|sqmi|sigfig=1}}, yet the greatest amount of loss of [[forest cover]] in the entire river system per square kilometer has occurred in this region due to heavy unchecked demand for natural resources. In the south of Yunnan, in [[Simao District|Simao]] and [[Xishuangbanna]] Prefectures, the river changes as the valley opens out, the floodplain becomes wider, and the river becomes wider and slower.

===Lower basin===
Major tributary systems develop in the lower basin. These systems can be separated into two groups: tributaries that contribute to the major wet season flows, and tributaries that drain low relief regions of lower rainfall. The first group are left bank tributaries that drain the high rainfall areas of Laos. The second group are those on the right bank, mainly the Mun and Chi Rivers, that drain a large part of northeast Thailand.

Laos lies almost entirely within the lower Mekong basin. Its climate, landscape and land use are the major factors shaping the hydrology of the river. The mountainous landscape means that only 16% of the country is farmed under lowland terrace or upland [[shifting cultivation]].<ref name="MRC_2005" /> With upland shifting agriculture (slash and burn), soils recover within 10 to 20 years but the vegetation does not. Shifting cultivation is common in the uplands of northern Laos and is reported to account for as much as 27% of the total land under rice cultivation.<ref name="MRC_2005" /> As elsewhere in the basin, forest cover has been steadily reduced during the last three decades by shifting agriculture and permanent agriculture. The cumulative impacts of these activities on the river regime have not been measured. However, the hydrological impacts of land cover changes induced by the [[Vietnam War]] were quantified in two sub-catchments of the lower Mekong River basin.<ref>{{cite journal |author1=G. Lacombe |author2=A. Pierret |author3=C. T. Hoanh |author4=O. Sengtaheuanghoung |author5=A. Noble |year=2010 |title=Conflict, migration and land-cover changes in Indochina: a hydrological assessment |journal=Ecohydrology |volume=3 |issue=4 |pages=382–391 |doi=10.1002/eco.166 |bibcode=2010Ecohy...3..382L |s2cid=131563940}}</ref>

Loss of forest cover in the Thai areas of the lower basin has been the highest of all the lower Mekong countries over the past 60 years. On the [[Khorat Plateau]], which includes the [[Mun River|Mun]] and [[Chi River|Chi]] tributary systems, forest cover was reduced from 42% in 1961 to 13% in 1993.<ref name="MRC_2005" /> Although this part of northeast Thailand has an annual rainfall of more than {{cvt|1000|mm|in|sigfig=1}}, a high evaporation rate means it is classified as a semi-arid region. Consequently, although the Mun and Chi basins drain 15% of the entire Mekong basin, they only contribute 6% of the average annual flow.<ref name="MRC_2005" /> Sandy and saline soils are the most common soil types, which makes much of the land unsuitable for wet rice cultivation. In spite of poor fertility, however, agriculture is intensive. Glutinous rice, maize, and cassava are the principal crops.<ref name="MRC_2005" /> Drought is by far the major hydrological hazard in this region.<ref name="MRC_2005" />
[[File:Mekong floating homes.jpg|thumb|Floating homes on the Mekong, Cambodia]]

As the Mekong enters Cambodia, over 95% of its flows have already joined the river.<ref name="MRC_2005" /> From here on downstream the terrain is flat and water levels rather than flow volumes determine the movement of water across the landscape. The seasonal cycle of changing water levels at [[Phnom Penh]] results in the unique "flow reversal" of water into and out of the Great Lake via the [[Tonle Sap River]]. Phnom Penh also marks the beginning of the delta system of the Mekong River. Here the mainstream begins to break up into an increasing number of branches.<ref name="MRC_2005" />

In Cambodia, wet rice is the main crop and is grown on the flood plains of the Tonle Sap, Mekong, and [[Bassac River|Bassac]] (the Mekong delta distributary known as the Hậu in Vietnam) Rivers.<ref name="MRC_2005" /> More than half of Cambodia remains covered with mixed evergreen and deciduous broadleaf forest, but forest cover has decreased from 73% in 1973 to 63% in 1993.<ref name="MRC_2005" /> Here, the river landscape is flat. Small changes in water level determine the direction of water movement, including the large-scale reversal of flow into and out of the Tonle Sap basin from the Mekong River.<ref name="MRC_2005" />
[[File:Mekong Delta river -a.jpg|thumb|upright|Mekong Delta, Vietnam]]

The [[Mekong Delta]] in Vietnam is farmed intensively and has little natural vegetation left. Forest cover is less than 10%. In the [[Central Highlands (Vietnam)|Central Highlands]] of Vietnam, forest cover was reduced from over 95% in the 1950s to around 50% in the mid-1990s.<ref name="MRC_2005" /> [[Agricultural expansion]] and [[population pressure]] are the major reasons for [[land use]] and landscape change. Both [[drought]] and [[flood]] are common hazards in the Delta, which many people believe is the most sensitive to upstream hydrological change.<ref name="MRC_2005" />

===Water flow along its course===
'''Table 1: Country share of Mekong River Basin (MRB) and water flows'''<ref name="MRC_2005" />
{| class="wikitable"
|-
|-
| || China || Myanmar || Laos || Thailand || Cambodia || Vietnam || Total
|-
| Basin area (km<sup>2</sup>) || 165,000 || 24,000 || 202,000 || 184,000 || 155,000 || 65,000 || 795,000
|-
| Catchment as % of MRB || 21 || 3 || 25 || 23 || 20 || 8 || 100
|-
| Flow as % of MRB || 16 || 2 || 35 || 18 || 18 || 11 || 100
|}

By taking into account hydrological regimes, physiography land use, and existing, planned and potential resource developments, the Mekong is divided into six distinct [[Reach (geography)|reaches]]:<ref name="MRC_2005"/>
[[File:2009-08-30 09-03 Luang Prabang 020 Mekong.jpg|thumb|The Mekong in Laos]]

''Reach 1: Lancang Jiang or Upper Mekong River in China''. In this part of the river, the major source of water flowing into the river comes from melting snow on the [[Tibetan plateau]]. This volume of water is sometimes called the "Yunnan component" and plays an important role in the low-flow hydrology of the lower mainstream. Even as far downstream as Kratie, the [[Yunnan]] component makes up almost 30% of the average dry season flow. A major concern is that the ongoing and planned expansion of dams and reservoirs on the Mekong mainstream in Yunnan could have a significant effect on the low-flow regime of the lower Mekong basin system.<ref name="MRC_2005"/><ref name=NYTimes2015-03-30>{{cite news |url=https://www.nytimes.com/2015/03/31/opinion/the-price-of-damming-tibets-rivers.html |title=The Price of Damming Tibet's Rivers |work=The New York Times |author=Michael Buckley |date=30 March 2015 |page=A25 |archive-url=https://web.archive.org/web/20150331103802/http://www.nytimes.com/2015/03/31/opinion/the-price-of-damming-tibets-rivers.html |archive-date=31 March 2015 |access-date=1 April 2015 |url-status=live |quote=Other plans call for diversion of water from the Brahmaputra, Salween and Mekong – all rivers that cross national boundaries.}}</ref><ref>{{cite journal |last1=Yeophantong |first1=Pichamon |title=China's Lancang Dam Cascade and Transnational Activism in the Mekong Region: Who's Got the Power? |journal=Asian Survey |volume=54 |issue=4 |doi=10.1525/as.2014.54.4.700 |year=2014 |pages=700–724}}</ref>

''Reach 2: [[Chiang Saen]] to [[Vientiane]] and [[Nong Khai]]''. This reach is almost entirely mountainous and covered with natural forest although there has been widespread slash and burn agriculture. Although this reach cannot be termed "unspoiled", the hydrological response is perhaps the most natural and undisturbed of all the lower basin. Many hydrological aspects of the lower basin start to change rapidly at the downstream boundary of this reach.<ref name="MRC_2005"/>

On 19 July 2019 this reach of the river dropped to its lowest level in a century. Officials are particularly concerned as July is in the wet season, when mainstream flows are abundant historically. Locals are blaming low water on the newly constructed [[Xayaburi Dam]], as it enters its test phase prior to the start of commercial operation in October 2019.<ref>{{cite news |title=Mekong River in Golden Triangle drops to lowest level in a century |url=https://www.thaipbsworld.com/mekong-river-in-golden-triangle-drops-to-lowest-level-in-a-century/ |access-date=21 July 2019 |work=Thai PBS |date=20 July 2019}}</ref>

''Reach 3: Vientiane and Nong Khai to [[Pakse]]''. The boundary between Reach 2 and 3 is where the Mekong hydrology starts to change. Reach 2 is dominated in both wet and dry seasons by the [[Yunnan]] Component. Reach 3 is increasingly influenced by contributions from the large left bank tributaries in Laos, namely the [[Nam Ngum]], [[Nam Theun]], Nam Hinboun, [[Xe Bang Fai River|Se Bang Fai]], Se Bang Hieng and Se Done Rivers. The [[Mun River|Mun]]-[[Chi River|Chi]] river system from the right bank in [[Thailand]] enters the mainstream within this reach.<ref name="MRC_2005"/>

''Reach 4: Pakse to [[Kratié (city)|Kratie]]''. The main hydrological contributions to the mainstream in this reach come from the [[Se Kong]], [[Se San]], and Sre Pok catchments. Together, these rivers make up the largest hydrological sub-component of the lower basin. Over 25% of the mean annual flow volume to the mainstream at Kratie comes from these three river basins. They are the key element in the hydrology of this part of the system, especially to the [[Tonle Sap]] flow reversal.<ref name="MRC_2005"/>

''Reach 5: Kratie to [[Phnom Penh]]''. This reach includes the hydraulic complexities of the Cambodian floodplain, the Tonle Sap and the Great Lake. By this stage, over 95% of the total flow has entered the Mekong system. The focus turns from hydrology and water discharge to the assessment of water level, over- bank storage and flooding and the hydrodynamics that determine the timing, duration and volume of the seasonal flow reversal into and out of the Great Lake.<ref name="MRC_2005"/>

''Reach 6: Phnom Penh to the [[South China Sea]]''. Here the mainstream divides into a complex and increasingly controlled and artificial system of branches and canals. Key features of flow behaviour are tidal influences and salt water intrusion. Every year, 35–50% of this reach is flooded during the rainy season. The impact of road embankments and similar infrastructure developments on the movement of this flood water is an increasingly important consequence of development.<ref name="MRC_2005"/>

Table 2 summarises the mean annual flows along the mainstream. The mean annual flow entering the lower Mekong from China is equivalent to a relatively modest {{cvt|450|mm|in}} depth of runoff. Downstream of Vientiane this increases to over {{cvt|600|mm|in}} as the principal left bank tributaries enter the mainstream, mainly the Nam Ngum and Nam Theun. The flow level falls again, even with the right bank entry of the Mun-Chi system from Thailand. Although the Mun–Chi basin drains 20% of the lower system, average annual runoff is only {{cvt|250|mm|in|0}}. Runoff in the mainstream increases again with the entry from the left bank of the Se Kong from southern Laos and [[Se San]] and Sre Pok from Vietnam and Cambodia.
[[File:CanThoFloatingMarket.jpg|thumb|Floating market, Cần Thơ, Mekong delta]]
[[File:CauKhi SongTien BinhDai BenTre VN.jpg|thumb|[[Cầu khỉ]] (monkey bridge) and small ''nước mắm'' (fish sauce) workshop on the bank of the [[Tiền River]] (branch of Mekong), Binh Dai District, [[Ben Tre Province]], Vietnam]]
[[File:PovertyHamlet Mekong@BenTre Vietnam.jpg|thumb|Hamlet, [[Tiền River]], Binh Dai District, [[Ben Tre Province]], Vietnam]]

'''Table 2: Lower Mekong Mainstream annual flow (1960 to 2004) at selected sites.'''<ref name="MRC_2005"/>
{| class="wikitable"
|-
! Mainstream site !! Catchment area (km<sup>2</sup>) !! Mean annual flow !! !! !! as % total Mekong
|-
| || || Discharge m<sup>3</sup>/s || Volume km<sup>3</sup> || Runoff (mm) ||
|-
| [[Chiang Saen District|Chiang Saen]] || 189,000 || 2,700 || 85 || 450 || 19
|-
| [[Luang Prabang]] || 268,000 || 3,900 || 123 || 460 || 27
|-
| [[Chiang Khan District|Chiang Khan]] || 292,000 || 4,200 || 133 || 460 || 29
|-
| [[Vientiane]] || 299,000 || 4,400 || 139 || 460 || 30
|-
| [[Nong Khai]] || 302,000 || 4,500 || 142 || 470 || 31
|-
| [[Nakhon Phanom]] || 373,000 || 7,100 || 224 || 600 || 49
|-
| [[Mukdahan]] || 391,000 || 7,600 || 240 || 610 || 52
|-
| [[Pakse]] || 545,000 || 9,700 || 306 || 560 || 67
|-
| [[Stung Treng]] || 635,000 || 13,100 || 413 || 650 || 90
|-
| [[Kratié (town)|Kratié]] || 646,000 || 13,200 || 416 || 640 || 91
|-
| Basin Total || 760,000 || 14,500 || 457 || 600 || 100
|}
Flows at Chiang Saen entering the lower basin from [[Yunnan]] make up about 15% of the wet season flow at [[Kratié (city)|Kratie]]. This rises to 40% during the dry season, even this far downstream. During the wet season, the proportion of average flow coming from Yunnan rapidly decreases downstream of Chiang Saen, from 70% to less than 20% at Kratie. The dry season contribution from Yunnan is much more significant. The major portion of the balance comes from Laos, which points to a major distinction in the low-flow hydrology of the river. One fraction comes from melting snow in China and [[Tibet]] and the rest from over-season catchment storage in the lower basin. This has implications for the occurrence of drought conditions. For example, if runoff from melting snow in any given year is very low, then flows upstream of [[Vientiane]]-[[Nong Khai]] would be lower.<ref name="MRC_2005"/>

In a large river system like the Mekong, seasonal flows can be quite variable from year to year. Although the pattern of the annual hydrograph is fairly predictable, its magnitude is not. The average monthly flows along the mainstream are listed in Table 3, providing an indication of their range and variability from year to year. At [[Pakse]], for example, flood season flows during August would exceed {{cvt|20000|m3/s|gal/s}} nine years out of ten, but exceed {{cvt|34000|m3/s|gal/s}} only one year in ten.<ref name="MRC_2005"/>

'''Table 3: Mekong Mainstream monthly discharge, 1960–2004''' (m<sup>3</sup>/s).<ref name="MRC_2005"/>
{| class="wikitable"
|-
! Month !! Chiang Saen !! Luang Prabang !! Vientiane !! Nakhon Phanom !! Mukdahan !! Pakse !! Kratie
|-
| Jan || 1,150 || 1,690 || 1,760 || 2,380 || 2,370 || 2,800 || 3,620
|-
| Feb || 930 || 1,280 || 1,370 || 1,860 || 1,880 || 2,170 || 2,730
|-
| Mar || 830 || 1,060 || 1,170 || 1,560 || 1,600 || 1,840 || 2,290
|-
| Apr || 910 || 1,110 || 1,190 || 1,530 || 1,560 || 1,800 || 2,220
|-
| May || 1,300 || 1,570 || 1,720 || 2,410 || 2,430 || 2,920 || 3,640
|-
| Jun || 2,460 || 3,110 || 3,410 || 6,610 || 7,090 || 8,810 || 11,200
|-
| Jul || 4,720 || 6,400 || 6,920 || 12,800 || 13,600 || 16,600 || 22,200
|-
| Aug || 6,480 || 9,920 || 11,000 || 19,100 || 20,600 || 26,200 || 35,500
|-
| Sep || 5,510 || 8,990 || 10,800 || 18,500 || 19,800 || 26,300 || 36,700
|-
| Oct || 3,840 || 5,750 || 6,800 || 10,200 || 10,900 || 15,400 || 22,000
|-
| Nov || 2,510 || 3,790 || 4,230 || 5,410 || 5,710 || 7,780 || 10,900
|-
| Dec || 1,590 || 2,400 || 2,560 || 3,340 || 3,410 || 4,190 || 5,710
|}

There is little evidence from the last 45 years of data of any systematic changes in the hydrological regime of the Mekong.<ref name="MRC_2005"/>

==Geology==
The internal drainage patterns of the Mekong are unusual when compared to those of other large rivers.<ref name="MRC_2010a" /> Most large river systems that drain the interiors of continents, such as the [[Amazon River|Amazon]], [[Congo River|Congo]], and [[Mississippi River|Mississippi]], have relatively simple [[wikt:dendritic|dendritic]] tributary networks that resemble a branching tree.<ref>{{cite journal |author1=M. Clark |author2=L. Schoenbohm |author3=L. Royden |author4=K. Whipple |author5=B. Burchfiel |author6=W. Zhang |author7=W. Tang |author8=E. Wang |author9=L. Chen |year=2004 |title=Surface uplift, tectonics, and erosion of eastern Tibet from large-scale drainage patterns |journal=[[Tectonics]] |volume=23 |issue=TC1006 |pages=227–234 |doi=10.1029/2002TC001402 |bibcode=2004Tecto..23.1006C|doi-access=free|url=http://ntur.lib.ntu.edu.tw/news/agent_contract.pdf }}</ref>

Typically, such patterns develop in basins with gentle slopes where the underlying geological structure is fairly homogeneous and stable, exerting little or no control on [[river morphology]].<ref name="Twidale2004">{{cite journal |author=C. Twidale|author-link=Charles Rowland Twidale |year=2004 |title=River patterns and their meanings |journal=[[Earth-Science Reviews]] |volume=67 |issue=3–4 |pages=159–218 |doi=10.1016/j.earscirev.2004.03.001 |bibcode=2004ESRv...67..159T}}</ref> In marked contrast, the tributary networks of the [[Salween River|Salween]], [[Yangtze River|Yangtze]], and particularly the Mekong, are complex with different sub-basins often exhibiting different, and distinct, drainage patterns. These complex drainage systems have developed in a setting where the underlying geological structure is heterogeneous and active, and is the major factor controlling the course of rivers and the landscapes they carve out.<ref>{{Cite book |author1=S. K. Tandon |author2=R. Sinha |name-list-style=amp |year=2007 |chapter=Geology of large river systems |pages=7–28 |editor=A. Gupta |title=Large rivers: geomorphology and management |location=London |publisher=[[John Wiley & Sons]] |isbn=978-0-470-84987-3}}</ref>

The elevation of the [[Tibetan Plateau]] during the Tertiary period was an important factor in the genesis of the south-west [[monsoon]],<ref name="CliftPlumb2008">{{cite book |author1=P. D. Clift |author2=A. R. Plumb |name-list-style=amp |year=2008 |title=The Asian monsoon: causes, history, and effects |location=Cambridge, UK |publisher=[[Cambridge University Press]] |isbn=9780521847995}}</ref> which is the dominant climatic control influencing the hydrology of the Mekong Basin. Understanding the nature and timing of the elevation of Tibet (and the [[Central Highlands (Vietnam)|Central Highlands]] of Vietnam) therefore helps explain the provenance of sediment reaching the delta and the [[Tonle Sap]] Great Lake today. Studies of the provenance of sediments in the Mekong delta reveal a major switch in the source of sediments about eight million years ago [[Year#SI prefix multipliers|(Ma)]].<ref>{{cite journal |author1=P. D. Clift |author2=A. Carter |author3=I. H. Campbell |author4=M. Pringle |author5=V. Nguyen |author6=C. Allen |author7=C. M. Allen |author8=K. V. Hodges |author9=T. T Mai |year=2006 |title=Thermochronology of mineral grains in the Red and Mekong Rivers, Viet Nam: Provenance and exhumation implications for Southeast Asia |journal=[[Geochemistry, Geophysics, Geosystems]] |volume=7 |issue=10 |pages=1–28 |doi=10.1029/2006GC001336 |bibcode=2006GGG.....710005C |url=https://eprints.bbk.ac.uk/28120/1/Clift_et_al-2006-Geochemistry%2C_Geophysics%2C_Geosystems.pdf |doi-access=free}}</ref><ref>{{cite journal |author=P. D. Clift, G. Layne & J. Blusztajn |year=2004 |title=Marine sedimentary evidence for monsoon strengthening, Tibetan uplift, and drainage evolution in East Asia |journal=[[Geophysical Monograph Series]] |volume=149 |issue=2004 |pages=255–282 |doi=10.1029/149GM14 |bibcode=2004GMS...149..255C |isbn=0-87590-414-9}}</ref> From 36 to 8 Ma the bulk (76%) of the sediments deposited in the delta came from erosion of the bedrock in the [[Three Parallel Rivers of Yunnan Protected Areas|Three Rivers Area]]. From 8 Ma to the present, however, the contribution from the Three Rivers Area fell to 40%, while that from the [[Central Highlands (Vietnam)|Central Highlands]] rose from 11 to 51%. One of the most striking conclusions of provenance studies is the small contribution of sediment from the other parts of the Mekong basin, notably the Khorat Plateau, the uplands of northern Laos and northern Thailand, and the mountain ranges south of the Three Rivers area.

The last glacial period came to an abrupt end about 19,000 years ago (19 [[Year#SI prefix multipliers|ka]]) when sea levels rose rapidly, reaching a maximum of about {{cvt|4.5|m|ft}} above present levels in the early Holocene about 8 ka.<ref name="Tamuraetal2004">{{cite journal |author1=T. Tamura |author2=Y. Saito |author3=S. Sotham |author4=B. Bunnarin |author5=K. Meng |author6=S. Im |author7=S. Choup |author8=F. Akiba |year=2009 |title=Initiation of the Mekong River Delta at 8 ka: Evidence from the sedimentary succession in the Cambodian lowland |journal=[[Quaternary Science Reviews]] |volume=28 |issue=3–4 |pages=327–344 |doi=10.1016/j.quascirev.2008.10.010 |bibcode=2009QSRv...28..327T}}</ref> At this time the shoreline of the [[South China Sea]] almost reached Phnom Penh and cores recovered from near Angkor Borei contained sediments deposited under the influence of tides, and salt marsh and mangrove swamp deposits.<ref name="Tamuraetal2004" /> Sediments deposited in the Tonle Sap Great Lake about this time (7.9–7.3 ka) also show indications of marine influence, suggesting a connection to the South China Sea.<ref>{{cite journal |author=D. Penny |year=2006 |title=The Holocene history and development of the Tonle Sap, Cambodia |journal=[[Quaternary Science Reviews]] |volume=25 |issue=3–4 |pages=310–322 |doi=10.1016/j.quascirev.2005.03.012 |bibcode=2006QSRv...25..310P}}</ref> Although the hydraulic relationships between the Mekong and the [[Tonle Sap]] Great Lake systems during the [[Holocene]] are not well understood, it is clear that between 9,000 and 7,500 years ago the confluence of the Tonle Sap and the Mekong was in proximity to the South China Sea.

The present river morphology of the Mekong Delta developed over the last 6,000 years.<ref name="MRC_2010a" /> During this period, the delta advanced {{cvt|200|km|mi}} over the continental shelf of the South China Sea, covering an area of more than {{cvt|62500|km2|mi2}}. From 5.3 to 3.5&nbsp;ka the delta advanced across a broad embayment formed between higher ground near the Cambodian border and uplands north of [[Ho Chi Minh City]]. During this phase of its development the delta was sheltered from the wave action of long-shore currents and was constructed largely through fluvial and tidal processes.<ref>{{cite journal |author1=T. K. Ta |author2=V. L. Nguyen |author3=M. Tateishi |author4=I. Kobayashi |author5=S. Tanabe |author6=Y. Saito |year=2002 |title=Holocene delta evolution and sediment discharge of the Mekong River, Southern Viet Nam |journal=[[Quaternary Science Reviews]] |volume=21 |issue=16–17 |pages=1807–1819 |doi=10.1016/S0277-3791(02)00007-0 |bibcode=2002QSRv...21.1807T}}</ref> At this time the delta was advancing at a rate of {{cvt|17|to|18|m|ft}} per year. After 3.5&nbsp;ka, however, the delta had built out beyond the embayment and became subject to wave action and marine currents. These deflected deposition south-eastwards in the direction of the [[Cà Mau Peninsula]], which is one of the most recent features of the delta.

For much of its length the Mekong flows through bedrock channels, i.e., channels that are confined or constrained by bedrock or old alluvium in the bed and riverbanks.<ref name="MRC_2010a" /> [[geomorphology|Geomorphologic]] features normally associated with the [[alluvial]] stretches of mature rivers, such as [[meander]]s, [[oxbow lake]]s, cut-offs, and extensive [[floodplains]] are restricted to a short stretch of the mainstream around [[Vientiane]] and downstream of [[Kratié (city)|Kratie]] where the river develops alluvial channels that are free of control exerted by the underlying bedrock.

The Mekong basin is not normally considered a seismically active area as much of the basin is underlain by the relatively stable continental block. Nonetheless, the parts of the basin in northern [[Laos]], northern [[Thailand]], [[Myanmar]] and China do experience frequent earthquakes and tremors. The magnitude of these earthquakes rarely exceeds 6.5 on the [[Richter magnitude scale]] and is unlikely to cause material damage.<ref>{{cite journal |author=C. H. Fenton, P. Charusiri & S. H. Wood |year=2003 |title=Recent paleoseismic investigations in northern and western Thailand |journal=[[Annals of Geophysics]] |volume=46 |issue=5 |pages=957–981 |hdl=2122/998}}</ref>{{Page needed|date=December 2015}}

==History==
[[File:1850 Perrot Map of Indo-Chine - Geographicus - Indochine-perrot-1825.jpg|left|thumb|19th century map showing the Mekong river as the "Mei-Kong" river]] 
The difficulty of navigating the river has meant that it has divided, rather than united, the people who live near it. The earliest known settlements date to 210 BCE, with [[Ban Chiang]] being an excellent example of early Iron Age culture. The earliest recorded civilization was the 1st century [[India]]nised-Khmer culture of [[Kingdom of Funan|Funan]], in the Mekong delta. Excavations at [[Oc Eo]], near modern [[An Giang]], have found coins from as far away as the [[Roman Empire]]. This was succeeded by the [[Khmer people|Khmer]] culture [[Chenla]] state around the 5th century. The [[Khmer empire]] of [[Angkor]] was the last great Indianized state in the region. From around the time of the fall of the Khmer empire, the Mekong was the front line between the emergent states of [[Thailand|Siam]] and Tonkin (North Vietnam), with Laos and Cambodia, then on the coast, torn between their influence.

The first European to encounter the Mekong was the [[Portugal|Portuguese]] [[António de Faria]] in 1540. A European map of 1563 depicts the river, although even by then little was known of the river upstream of the delta. European interest was sporadic: the [[Spain|Spanish]] and Portuguese mounted some missionary and trade expeditions, while the Dutch Gerrit van Wuysthoff led an expedition up the river as far as Vientiane in 1641–42.

The French invaded the region in the mid-19th century, capturing [[Saigon]] in 1861, and establishing a protectorate over Cambodia in 1863.
[[File:Mekongmembersangkor.jpg|thumb|left|Members of the [[Mekong expedition of 1866–1868]]]]

The first systematic European exploration began with the [[Mekong expedition of 1866–1868|French Mekong Expedition]] led by [[Ernest Doudard de Lagrée]] and [[Francis Garnier]], which ascended the river from its mouth to [[Yunnan]] between 1866 and 1868. Their chief finding was that the Mekong had too many falls and rapids to ever be useful for [[navigation]]. The river's source was found by [[Pyotr Kuzmich Kozlov]] in 1900.

From 1893, the French extended their control of the river into Laos, establishing [[French Indochina]] by the first decade of the 20th century. This lasted until the [[First Indochina War|First]] and [[Vietnam War|Second]] Indochina Wars expelled French from its former colony and defeated US-supported governments.

During the wars in Indochina in the 1970s, a significant quantity of explosives (sometimes, entire barges loaded with military [[Artillery|ordnance]]) sank in the Cambodian section of the Mekong (as well as in the country's other waterways). Besides being a danger for fishermen, unexploded ordnance also creates problems for bridge and irrigation systems construction. As of 2013, Cambodian volunteers are being trained, with the support of the Office of Weapons Removal and Abatement within the [[Bureau of Political-Military Affairs|US State Department Bureau of Political-Military Affairs]], to conduct underwater explosive removal.<ref>[http://www.globalpost.com/dispatch/news/regions/asia-pacific/cambodia/130321/landmines-demining-scuba-diving Cambodia: Demining in the depths] {{Webarchive|url=https://web.archive.org/web/20130325025350/http://www.globalpost.com/dispatch/news/regions/asia-pacific/cambodia/130321/landmines-demining-scuba-diving |date=25 March 2013 }}. Denise Hruby, 24 March 2013</ref>

The many maps of the river basin produced throughout recorded history reflect the region's changing human geography and politics.<ref>{{Cite book |last=Romanos |first=Christoforos |url=https://surfdrive.surf.nl/files/index.php/s/LuWmXSpftRz6Z7p |title=Liquid Territories : configurations of geographic space in the cartographic projections of the Mekong River's catchment areas |publisher=Delft University of Technology |year=2023 |location=Delft |pages=325 |language=en}}</ref>

In 1995, Laos, Thailand, Cambodia, and Vietnam established the [[Mekong River Commission]] (MRC) to manage and coordinate the use and care of the Mekong. In 1996 China and Myanmar became "dialogue partners" of the MRC and the six countries now work together in a cooperative framework. In 2000, the governments of China, Laos, Thailand and Myanmar signed a ''Agreement on Commercial Navigation on Lancang-Mekong River among the Governments of the People's Republic of China, the Lao People's Democratic Republic, the Union of Myanmar and the Kingdom of Thailand'' which is the mechanism for cooperation with regard to riverine trade on the upper stretches of the Mekong.<ref>{{cite book |last1=Lazarus |first1=K. |last2=Dubeau |first2=P. |last3=Bambaradeniya |first3=C. |last4=Friend |first4=R. |last5=Sylavong |first5=L. |title=An Uncertain Future: Biodiversity and Livelihoods Along the Mekong River in Northern Lao PDR|chapter-url=https://portals.iucn.org/library/sites/library/files/documents/2006-060.pdf |access-date=21 August 2019 |year=2006 |publisher=The World Conservation Union (IUCN) |location=Bangkok, Thailand and Gland, Switzerland |isbn=978-2-8317-0956-7 |pages=21–24 |chapter=Increasing pace of change}}</ref><ref>{{cite web |url=https://www.jcccn.org/images/rule/Agreement.pdf |title=Agreement on Commercial Navigation on Lancang-Mekong River among the Governments of the People's Republic of China, the Lao People's Democratic Republic, the Union of Myanmar and the Kingdom of Thailand |date=20 April 2000 |publisher=JCCN |access-date=21 August 2019 |archive-date=21 August 2019 |archive-url=https://web.archive.org/web/20190821103234/https://www.jcccn.org/images/rule/Agreement.pdf |url-status=dead}}</ref>

==Natural history==
[[File:Pelochelys cantorii.jpg|thumb|Extirpated from most of its pan-Asian range, [[Cantor's giant softshell turtle]] can still be found along a stretch of the Mekong in Cambodia (Khmer called "Kanteay")]]

The Mekong basin is one of the richest areas of biodiversity in the world. Only the [[Amazon Basin|Amazon]] boasts a higher level of bio-diversity.<ref name="MRC_2010a" /> Biota estimates for the [[Greater Mekong Subregion]] (GMS) include 20,000 plant species, 430 mammals, 1,200 birds, 800 reptiles and amphibians,<ref>{{cite web |author=C. Thompson |year=2008 |title=First Contact in the Greater Mekong |publisher=[[World Wide Fund for Nature|WWF]] Greater Mekong Program |url=http://www.wwf.dk/dk/Service/Bibliotek/WWF+i+Asien/Rapporter+mv./First+Contact+in+the+Greater+Mekong |format=[[Portable Document Format|PDF]]}}{{Dead link|date=August 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> and an estimated 850 freshwater fish species (excluding [[euryhaline]] species mainly found in salt or [[brackish]] water, as well as [[introduced species]]).<ref>{{cite web |author=K. G. Hortle |year=2009 |title=Fishes of the Mekong – how many species are there? |publisher=[[Mekong River Commission]] |series=Catch and Culture |url=http://ns1.mrcmekong.org/Catch-Culture/vol15_2Aug09/fishes-of-the-Mekong.htm |url-status=dead |archive-url=https://web.archive.org/web/20120730123927/http://ns1.mrcmekong.org/Catch-Culture/vol15_2Aug09/fishes-of-the-Mekong.htm |archive-date=30 July 2012}}</ref> The most [[Species richness|species rich]] orders among the freshwater fish in the river basin are [[Cypriniformes|cypriniforms]] (377 species) and [[catfish]] (92 species).<ref name=FishValbo>Valbo-Jørgensen, J; Coates, D.; and Hortle, K. (2009). ''Fish diversity in the Mekong River basin.'' pp. 161–196 in: Campbell, I.C. (editor). The Mekong – Biophysical Environment of an International River Basin, 1st edition. Academic Press, Elsevier. {{ISBN|978-0-12-374026-7}}</ref>

[[New species]] are regularly described from the Mekong. In 2009, 145 species previously unknown to science were described from the region, including 29 fish species, 2 bird species, 10 reptiles, 5 mammals, 96 plants, and 6 amphibians.<ref>{{cite web |author1=N. Gephart |author2=G. Blate |author3=C. McQuistan |author4=C. Thompson |year=2010 |title=New Blood: Greater Mekong New Species Discoveries, 2009 |publisher=[[World Wide Fund for Nature|WWF]] |url=http://awsassets.panda.org/downloads/greater_mekong_species_report_web_version_report_1_oct_2010.pdf}}</ref> Between 1997 and 2015, an average of two new species per week were discovered in the region.<ref>{{cite news |title=163 new species, including 'Klingon Newt', discovered |url=http://www.foxnews.com/science/2016/12/20/163-new-species-including-klingon-newt-discovered.html |access-date=20 December 2016 |publisher=[[Fox News]] |date=20 December 2016}}</ref> The Mekong Region contains 16 [[World Wide Fund for Nature|WWF]] [[Global 200]] ecoregions, the greatest concentration of ecoregions in mainland Asia.<ref name="MRC_2010a" />

No other river is home to so many species of very large fish.<ref name=WWF2012>{{cite web |year=2012 |title=River of Giants: Giant Fish of the Mekong |publisher=[[World Wide Fund for Nature|WWF]] Greater Mekong Program |url=http://assets.worldwildlife.org/publications/321/files/original/River_of_Giants_Giant_Fish_of_the_Mekong.pdf}}</ref> The biggest include three species of ''[[Probarbus]]'' barbs, which can grow up to {{cvt|1.5|m|ft|0}} and weigh {{cvt|70|kg|lb|-1}},<ref>{{FishBase genus |genus=Probarbus |month=February |year=2017}}</ref> the [[giant freshwater stingray]] (''Himantura polylepis'', [[syn.]] ''H. chaophraya''), which can reach at least {{cvt|5|m|ft}} in length and {{cvt|1.9|m|ftin}} in width,<ref>{{cite book |author1=Last, P.R. |author2=Compagno, L.J.V. |chapter=Myliobatiformes: Dasyatidae |editor1=Carpenter, K.E. |editor2=Niem, V.H. |title=FAO identification guide for fishery purposes. The living marine resources of the Western Central Pacific |publisher=Food and Agriculture Organization of the United Nations |year=1999 |isbn=92-5-104302-7 |pages=1479–1505}}</ref> the [[giant pangasius]] (''Pangasius sanitwongsei''), [[giant barb]] (''Catlocarpio siamensis'') and the [[Endemism|endemic]] [[Mekong giant catfish]] (''Pangasianodon gigas''). The last three can grow up to about {{cvt|3|m|ft|0}} in length and weigh {{cvt|300|kg|lb}}.<ref name=WWF2012/> All of these have declined drastically because of dams, flood control, and overfishing.<ref name=WWF2012/>

One species of [[freshwater dolphin]], the [[Irrawaddy dolphin]] (''Orcaella brevirostris''), was once common in the whole of the lower Mekong but is now very rare, with only 85 individuals remaining.<ref name=Ryan>{{cite journal |year=2011 |title=Irrawaddy dolphin demography in the Mekong River: an application of mark–resight models |journal=Ecosphere |volume=2 |issue=5 |page=art58 |author1=Ryan, Gerard Edward |author2=Dove, Verne |author3=Trujillo, Fernando |author4=Doherty, Paul F. |doi=10.1890/ES10-00171.1|doi-access=free|bibcode=2011Ecosp...2...58R |s2cid=59130504 |url=http://pdfs.semanticscholar.org/5937/aedf2c9e4c1dcae375ca9186969b9a0b68c7.pdf }}</ref>

Among other wetland mammals that have been living in and around the river are the [[smooth-coated otter]] (''Lutra perspicillata'') and [[fishing cat]] (''Prionailurus viverrinus'').

The endangered [[Siamese crocodile]] (''Crocodylus siamensis'') occurs in small isolated pockets within the northern Cambodian and Laotian portions of the Mekong River. The [[saltwater crocodile]] (''Crocodylus porosus'') once ranged from the Mekong Delta up the river into Tonle Sap and beyond but is now extinct in the river, along with being extinct in all of Vietnam and possibly even Cambodia.

===Protected areas===
*The headwaters of the Mekong in [[Zadoi County]], Qinghai, China, are protected in [[Sanjiangyuan National Nature Reserve]]. The name Sanjiangyuan means "the sources of the Three Rivers". The reserve also includes the headwaters of the [[Yellow River]] and the [[Yangtze]].
*The section of the river flowing through deep gorges in [[Yunnan]] Province is part of the [[Three Parallel Rivers of Yunnan Protected Areas]], a UNESCO [[World Heritage Site]].
*The [[Tonle Sap Biosphere Reserve]] in Cambodia contains the largest lake in Southeast Asia. It is a UNESCO [[Biosphere reserve]].
[[File:Bank Erosion at Song Tien of Mekong, Binh Dai, Ben Tre, Vietnam.jpg|thumb|Bank erosion on the Song Tien, a Mekong branch, Binh Dai District, Ben Tre Province, Vietnam.]]

===Natural phenomena===
The low tide level of the river in Cambodia is lower than the high tide level out at sea, and the flow of the Mekong inverts with the tides throughout its stretch in Vietnam and up to Phnom Penh. The very flat Mekong delta area in Vietnam is thus prone to flooding, especially in the provinces of An Giang and Dong Thap (Đồng Tháp), near the Cambodian border.

==Fisheries==
[[File:FishFarming on Mekong- Song Tien Vietnam.jpg|thumb|Fish Farming on Mekong branch, Song Tien, [[Đồng Tháp Province]], Vietnam]]

Aquatic biodiversity in the Mekong River system is the second highest in the world after the [[Amazon River|Amazon]].<ref name="ICEM2010">{{cite web |author=International Center for Environmental Management |year=2010 |title=Strategic Environmental Assessment (SEA) of hydropower on the Mekong mainstream |publisher=[[Mekong River Commission]] |url=http://www.mrcmekong.org/assets/Publications/Consultations/SEA-Hydropower/SEA-Main-Final-Report.pdf}}</ref><ref name="Fergusonetal2011">{{cite journal |author1=J.W. Ferguson |author2=M. Healey |author3=P. Dugan |author4=C. Barlow |year=2011 |title=Potential Effects of Dams on Migratory Fish in the Mekong River: Lessons from the Fraser and Columbia Rivers. |journal=[[Environmental Management]] |volume=47 |issue=1 |pages=141–159 |doi=10.1007/s00267-010-9563-6 |pmid=20924582 |bibcode=2011EnMan..47..141F |s2cid=19900859}}</ref>
The Mekong boasts the most concentrated [[biodiversity]] per hectare of any river.<ref name="VJetal2009">{{cite book |author1=J. Valbo-Jørgensen, D. Coates |author2=K.G. Hortle|name-list-style=amp |year=2009 |chapter=Fish diversity in the Mekong River Basin. |editor=I.C. Campbell |title=The Mekong: Biophysical Environment of an International River Basin. |location=London |publisher=[[Elsevier Publishers]] |pages=161–196 |isbn=978-0123740267}}</ref> The largest recorded freshwater fish, a {{cvt|300|kg|lb}} [[giant freshwater stingray]] in 2022 and previously a {{cvt|293|kg|lb}} [[Mekong giant catfish]] in 2005, were both caught in the Mekong River.<ref>{{Cite web |agency=Associated Press |date=2022-06-20 |title=Largest freshwater fish ever recorded caught in Cambodia |url=https://www.theguardian.com/environment/2022/jun/20/largest-freshwater-fish-ever-recorded-caught-in-cambodia |access-date=2022-06-20 |website=the Guardian |language=en}}</ref>

The commercially valuable fish species in the Mekong are generally divided between "black fish", which inhabit low oxygen, slow moving, shallow waters, and "white fish", which inhabit well oxygenated, fast moving, deeper waters.<ref name="MRC_2010b">{{cite web |author=Mekong River Commission |year=2010 |title=Assessment of Basin-wide Development Scenarios: Technical Note 11: Impacts on Fisheries |publisher=[[Mekong River Commission]] |url=http://www.mrcmekong.org/assets/Other-Documents/BDP/Assessment-of-Basin-wide-dev-Scenarios-MainReport-2011.pdf |author-link=Mekong River Commission}}{{dead link|date=June 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> People living within the Mekong River system generate many other sources of food and income from what are often termed "other aquatic animals" (OAAs) such as freshwater crabs, shrimp, snakes, turtles, and frogs.

OAAs account for about 20% of the total Mekong catch.<ref name="MRC_2010a"/> When fisheries are discussed, catches are typically divided between the wild capture fishery (i.e., fish and other aquatic animals caught in their natural habitat), and aquaculture (fish reared under controlled conditions). Wild capture fisheries play the most important role in supporting livelihoods. Wild capture fisheries are largely open access fisheries, which poor rural people can access for food and income.

Broadly, there are three types of fish habitats in the Mekong: i) the river, including all the main tributaries, rivers in the major flood zone, and the Tonle Sap, which altogether yield about 30% of wild catch landings; ii) rain-fed wetlands outside the river-floodplain zone, including mainly rice paddies in formerly forested areas and usually inundated to about {{cvt|50|cm|in}}, yielding about 66% of wild catch landings; and iii) large water bodies outside the flood zone, including canals and reservoirs yielding about 4% of wild catch landings.<ref name="MRC_2010a"/>

The Mekong Basin has one of the world's largest and most productive inland fisheries.<ref name="ICEM2010" /><ref name="Baran&Myschowoda2009">{{cite journal |author1=E. Baran |author2=C. Myschowoda |name-list-style=amp |year=2009 |title=Dams and fisheries in the Mekong Basin |journal=[[Aquatic Ecosystem Health and Management]] |volume=12 |issue=3 |pages=227–234 |doi=10.1080/14634980903149902 |bibcode=2009AqEHM..12..227B |s2cid=85279301}}</ref><ref name="Baran&Ratner2007">{{cite web |author1=E. Baran |author2=B. Ratner |name-list-style=amp |year=2007 |title=The Don Sahong Dam and Mekong Fisheries |publisher=[[World Fish Center]] |series=Science Brief |url=http://www.worldfishcenter.org/resource_centre/DonSahong-final.pdf |access-date=12 October 2012 |archive-url=https://web.archive.org/web/20130509120231/http://www.worldfishcenter.org/resource_centre/DonSahong-final.pdf |archive-date=9 May 2013 |url-status=dead}}</ref><ref name="Sarkkulaetal2009">{{cite book |author=J. Sarkkula, M. Keskinen, J. Koponen, M. Kummu, J. E. Richery & O. Varis |year=2009 |chapter=Hydropower in the Mekong Region: What Are the Likely Impacts Upon Fisheries? |editor1=F. Molle |editor2=T. Foran |editor3=M. Käkönen |title=Contested Waterscapes in the Mekong Region: Hydropower, Livelihoods and Governance |location=London |publisher=[[Earthscan]] |pages=227–249 |isbn=978-1-84407-707-6}}</ref> An estimated two million tonnes of fish are landed a year, in addition to almost 500,000 tonnes of other aquatic animals.<ref name="Hortle2007">{{cite web |author=K. G. Hortle |year=2007 |title=Consumption and the yield of fish and other aquatic animals from the Lower Mekong Basin |publisher=[[Mekong River Commission]] |series=MRC Technical Paper No. 16 |url=http://www.mrcmekong.org/assets/Publications/technical/tech-No16-consumption-n-yield-of-fish.pdf}}</ref> Aquaculture yields about two million tonnes of fish a year.<ref name="MRC_2010b" /> Hence, the lower Mekong basin yields about 4.5 million tonnes of fish and aquatic products annually. The total economic value of the fishery is between US$3.9 and US$7 billion a year.<ref name="MRC_2010a"/> Wild capture fisheries alone have been valued at US$2 billion a year.<ref name="Baran&Ratner2007" /> This value increases considerably when the multiplier effect is included, but estimates vary widely.

An estimated 2.56 million tonnes of inland fish and other aquatic animals are consumed in the lower Mekong every year.<ref name="MRC_2010b" /> Aquatic resources make up between 47 and 80% of animal protein in rural diets for people who live in the Lower Mekong Basin.<ref name="Baran&Ratner2007" /><ref name="Bush2003">{{cite web |author=S. Bush |year=2007 |title=Give a man a fish..." Contextualising Living Aquatic Resources Development in the Lower Mekong Basin |publisher=Australian Mekong Resource Centre, [[University of Sydney]] |series=AMRC Working Papers 8 |url=http://sydney.edu.au/mekong/documents/wp8.pdf}}</ref><ref name="Friend&Blake2009">{{cite journal |author1=R. Friend |author2=D. J. H. Blake |name-list-style=amp |year=2009 |title=Negotiating trade-offs in water resources development in the Mekong Basin: implications for fisheries and fishery-based livelihoods |journal=[[Water Policy]] |volume=11 |issue=S1 |pages=13–30 |doi=10.2166/wp.2009.001}}</ref> Fish are the cheapest source of animal protein in the region and any decline in the fishery is likely to significantly impact nutrition, especially among the poor.<ref name="ICEM2010" /><ref name="Bush2003" /><ref name="Baird_2009a">{{cite web |author=I. G. Baird |year=2009 |title=The Don Sahong Dam: Potential Impacts on Regional Fish Migrations, Livelihoods and Human Health |publisher=POLIS Project on Environmental Governance, [[University of Victoria]] |url=http://polisproject.org/PDFs/Baird%_Don%20Sahong.pdf}}{{dead link|date=July 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref name="Baird_2011">{{cite journal |author=I. G. Baird |year=2011 |title=The Don Sahong Dam |journal=[[Critical Asian Studies]] |volume=43 |issue=2 |pages=211–235 |doi=10.1080/14672715.2011.570567 |s2cid=55168234}}</ref> Fish are the staple of the diet in Laos and Cambodia, with around 80% of the Cambodian population's annual protein intake coming from fish caught in the Mekong River system, with no alternative source to replace it. An MRC report claims that dam projects on the Mekong River will reduce aquatic life by 40% by 2020, and predicted that 80% of fish will be depleted by 2040. Thailand will be impacted, as its fish stocks in the Mekong will decline by 55%, Laos will be reduced by 50%, Cambodia by 35%, and Vietnam by 30%.<ref name="BP-20190720">{{cite news |last1=Wipatayotin |first1=Apinya |title=Dam tests spark crisis |url=https://www.bangkokpost.com/thailand/general/1715627/dam-tests-spark-crisis |access-date=20 July 2019 |work=[[Bangkok Post]] |date=20 July 2019}}</ref>

It is estimated that 40 million rural people, more than two-thirds of the rural population in the lower Mekong basin, are engaged in the wild capture fishery.<ref name="MRC_2010a" /> Fisheries contribute significantly to a diversified livelihood strategy for many people, particularly the poor, who are highly dependent on the river and its resources for their livelihoods.<ref name="Baran&Myschowoda2009" /><ref name="Baran&Ratner2007" /><ref name="Friend&Blake2009" /> They provide a principal form of income for numerous people and act as a safety net and coping strategy in times of poor agricultural harvests or other difficulties.<ref name="Baran&Myschowoda2009" /><ref name="Baran&Ratner2007" /><ref name="Friend&Blake2009" /> In Laos alone, 71% of rural households (2.9 million people) rely on fisheries for either subsistence or additional cash income. Around the [[Tonle Sap Lake]] in Cambodia, more than 1.2 million people live in fishing communes and depend almost entirely on fishing for their livelihoods.<ref name="MRC_2010a" />

==Dams{{anchor|River_modifications}}==
{{Main|Hydropower in the Mekong River Basin}}

Dams in the Mekong reference those built for hydropower, irrigation and other uses (such as water supply). As of February 2024, dams in the Mekong are distributed as follows:

Table 4: Dams in the Mekong River Basin

{| class="wikitable"
|-
! Territory !! HPPs !! Irrigation Dams !! Others !! Total
|-
| [[Cambodia]] || 1 || 9 || 1 || 11 
|-
| [[Yunnan]] || 26 || 25 || 10 || 61
|- 
| [[Tibet Autonomous Region|TAR]] || 4 || 0 || 0 || 4
|-
| [[Laos]] || 56 || 4 || 6 || 66
|-
| [[Myanmar]] || 1 || 0 || 0 || 1
|-
| [[Thailand]] || 7 || 159 || 2 || 168
|-
| [[Vietnam]] || 26 || 33 || 1 || 60
|-
| Total || 121 || 230 || 20 || 371
|}

'''Notes''': HPPs = Hydropower Plants. Data calculated from the CGIAR Research Program on Water, Land and Ecosystems - Greater Mekong 'Dataset on the Dams of the Irrawaddy, Mekong, Red and Salween River Basins'. Only HPPs with an installed capacity of 15 Megawatts (MW) or more are included; and/or dams with a reservoir area of 0.5 km<sup>2</sup> or more. 

There are also multiple HPPs under construction within the basin. As of February 2024, there is one under construction in Cambodia, three in the [[Tibet Autonomous Region|TAR]], and 14 in [[Laos]].

Of the Mekong's HPPs, 15 are located on the [[Hydropower in the Mekong River Basin#Mekong_mainstream_hydropower_plants|Mekong mainstream]]. Of these, 13 are in China, and two in Laos. An additional mainstream dam is currently under construction in Laos, and another in China.

==Navigation==
[[File:Mekong ferry-1.JPG|thumb|Mekong ferry, Neak Loeung, Cambodia]]
[[File:Oudomxay Pakbeng3 tango7174.jpg|thumb|Slow cruise boats, [[Pakbeng]], [[Laos]]]]

For thousands of years the Mekong River has been an important conduit for people and goods between the many towns on its banks. Traditional forms of trade in small boats linking communities continue today, however the river is also becoming an important link in international trade routes, connecting the six Mekong countries to each other, and also to the rest of the world.<ref name="MRC_2010a" /> The Mekong is still a wild river and navigation conditions vary greatly along its length. Broadly, navigation of the river is divided between upper and lower Mekong, with the "upper" part of the river defined as the stretch north of the [[Khone Falls]] in southern Laos and the "lower" part as the stretch below these falls.

Narrower and more turbulent sections of water in the upstream parts of the Mekong River, coupled with large annual water level variations continue to present a challenge to navigation. The seasonal variations in water level directly affect trade in this section of the river. Volumes of trade being shipped decrease by more than 50%, primarily due to the reduced draughts available during the low water season (June–January).<ref name="MRC_2010a" /> Despite these difficulties, the Mekong River is already an important link in the transit chain between [[Kunming]] and [[Bangkok]] with about 300,000 tonnes of goods shipped via this route each year.<ref name="MRC_2010a" /> The volume of this trade is expected to increase by 8–11% per year. Port infrastructure is being expanded to accommodate the expected growth in traffic, with new facilities planned for [[Chiang Saen District|Chiang Saen]] port.<ref name="MRC_2010a" />

In Laos, 50 and 100 [[Deadweight tonnage|DWT]] vessels are operated for regional trade. Cargos carried are timber, agricultural products, and construction materials.<ref name="MRC_2010a" /> Thailand imports a wide variety of products from China, including vegetables, fruit, agricultural products, and fertilisers. The main exports from Thailand are dried [[longan]], fish oil, rubber products, and consumables. Nearly all the ships carrying cargo to and from Chiang Saen Port are 300 DWT Chinese flag vessels.<ref name="MRC_2010a" />

Waterborne trade in the lower Mekong countries of Vietnam and Cambodia has grown significantly, with trends in container traffic at [[Phnom Penh]] port and general cargo through [[Can Tho]] port both showing steady increases until 2009 when a decrease in cargo volumes can be attributed to the global financial crisis and a subsequent decline in demand for the export of garments to the US.<ref name="MRC_2010a" /> In 2009, Mekong trade received a significant boost with the opening of a new deep-water port at [[Cai Mep]] in Vietnam. This new port has generated a renewed focus on the Mekong River as a trade route. The Cai Mep container terminals can accommodate vessels with a draught of {{cvt|15.2|m|ft}}, equivalent to the largest container ships in the world. These mother vessels sail directly to Europe or the United States, which means that goods can be shipped internationally to and from Phnom Penh with only a single transshipment at Cai Mep.<ref name="MRC_2010a" />

As an international river, a number of agreements exist between the countries that share the Mekong to enable trade and passage between them. The most important of these, which address the full length of the river, are:<ref name="MRC_2010a" />
*Agreement between China and Lao PDR on Freight and Passenger Transport along the Lancang–Mekong River, adopted in November 1994.
*Agreement on the Cooperation for the Sustainable Development of the Mekong River Basin, Article 9, Freedom of Navigation, 5 April 1995, Chiang Rai.
*Hanoi Agreement between Cambodia and Viet Nam on Waterway Transportation, 13 December 1998.
*Agreement between and among the Governments of the Laos, Thailand, and Vietnam for Facilitation of Cross border Transport of Goods and People, (amended at Yangon, Myanmar), signed in Vientiane, 26 November 1999.
*Agreement on Commercial Navigation on Lancang–Mekong River among the governments of China, Laos, Myanmar and Thailand, adopted at Tachileik, 20 April 2000.
*Phnom Penh Agreement between Cambodia and Vietnam on the Transit of Goods, 7 September 2000.
*New Agreement on Waterway Transportation between Vietnam and Cambodia, signed in Phnom Penh, 17 December 2009.

In December 2016, the Thai cabinet of Prime Minister [[Prayut Chan-o-cha]] agreed "in principle" to a plan to dredge stretches of the Mekong and demolish rocky outcrops that are hindrances to easy navigation. The international Lancang-Mekong River navigation improvement plan for 2015–2025, conceived by China, Myanmar, Lao, and Thailand, aims to make the river more navigable for 500-tonne cargo vessels sailing the river from [[Yunnan]] to [[Luang Prabang]], a distance of {{cvt|890|km|mi}}.<ref name="BP-20170109">{{cite news |last1=Suksamran |first1=Nauvarat |title=Locals slam Mekong blasting plan |url=http://www.bangkokpost.com/news/general/1176681/locals-slam-mekong-blasting-plan |access-date=9 January 2017 |work=Bangkok Post |date=9 January 2017}}</ref> China has been the driving force behind the demolition plan as it aims to expand trade in the area.<ref>{{cite news |title=Spare the Mekong |url=http://www.bangkokpost.com/opinion/opinion/1171213/spare-the-mekong |access-date=30 December 2016 |work=Bangkok Post |date=30 December 2016 |format=Opinion}}</ref> The plan is split into two phases. The first phase, from 2015 to 2020, involves a survey, a design, and an assessment of the environmental and social impacts of the project. These have to be approved by the four countries involved: China, Laos, Myanmar, Thailand. The second phase (2020–2025) involves navigational improvements from [[Simao District|Simao]] in China to 243 border posts in China and Myanmar, a distance of {{cvt|259|km|mi}}.<ref name="BP-20170109"/> Local groups have countered that native inhabitants already operate their boats year-round and that the plan to blast the rapids is not about making life better for local people, but about enabling year-round traffic of large Chinese commercial boats.<ref name="BPO-20190717">{{cite news |last1=Roykaew |first1=Niwat |title=China must be sincere on Mekong |url=https://www.bangkokpost.com/opinion/opinion/1713756#cxrecs_s |access-date=20 July 2019 |work=Bangkok Post |date=17 July 2019 |format=Opinion}}</ref>

On 4 February 2020, the Thai Cabinet voted to stop the project to blast and dredge {{cvt|97|km|mi}} of the river bed after Beijing failed to stump up the money for further surveys of the affected area.<ref>{{cite news |title=Thais ditch China-led plan to dredge Mekong |url=https://www.straitstimes.com/asia/se-asia/thais-ditch-china-led-plan-to-dredge-mekong |access-date=6 February 2020 |work=The Straits Times |date=6 February 2020}}</ref>

==Bridges==
{{see also|List of crossings of the Mekong River}}
[[File:Kizuna Bridge 2020.jpg|thumb|Kizuna Bridge cross Mekong at Kampong Cham]]
Construction of Myanmar–Laos Friendship Bridge started on 19 February 2013. The bridge will be {{cvt|691.6|m}} long and have an {{cvt|8.5|m|adj=on}} wide two-lane motorway.<ref>{{Cite web |url=http://news.xinhuanet.com/english/world/2013-02/19/c_132177630.htm |title=Myanmar, Laos start building Mekong River friendship bridge - Xinhua &#124; English.news.cn |access-date=17 March 2013 |archive-url=https://web.archive.org/web/20130225054526/http://news.xinhuanet.com/english/world/2013-02/19/c_132177630.htm |archive-date=25 February 2013 |url-status=dead}}</ref>

The [[Thai–Lao Friendship Bridge]] ({{langx|th|สะพานมิตรภาพ ไทย-ลาว}}, {{rtgs|''Saphan Mittraphap Thai-Lao''}}) connects [[Nong Khai]] city with [[Vientiane]] in Laos. The {{cvt|1170|m|ft|adj=mid|-long}} bridge opened on 8 April 1994. It has two {{cvt|3.5|m|ft|adj=mid|-wide}} lanes with a single railway line in the middle. On 20 March 2004, the Thai and Lao governments agreed to extend the railway to Tha Nalaeng in Laos. This extension has since been completed.

The [[Second Thai–Lao Friendship Bridge]] connects [[Mukdahan]] to [[Savannakhet]]. The two-lane, {{cvt|12|m|ft|adj=mid|-wide}}, {{cvt|1600|m|ft|adj=mid|-long}} bridge opened to the public on 9 January 2007.

The [[Third Thai–Lao Friendship Bridge]] opened for traffic on 11 November 2011, connecting [[Nakhon Phanom Province]] (Thailand) and [[Thakhek]] (Laos), as part of [[Asian Highway 3]]. The Chinese and Thai governments agreed to build the bridge and share the estimated US$33 million cost.

The [[Fourth Thai–Lao Friendship Bridge]] opened to traffic on 11 December 2013.<ref>{{Cite web |url=http://www.vientianetimes.org.la/FreeContent/FreeConten_Ceremony.htm |title=vientianetimes.org |access-date=17 March 2013 |archive-url=https://web.archive.org/web/20121229225059/http://www.vientianetimes.org.la/FreeContent/FreeConten_Ceremony.htm |archive-date=29 December 2012 |url-status=dead}}</ref> It links [[Chiang Rai Province]], Thailand with [[Ban Houayxay]], Laos.

There is one bridge over the Mekong entirely within Laos. Unlike the Friendship Bridges, it is not a border crossing. It is at [[Pakse]] in [[Champasak Province]]. It is {{cvt|1380|m|ft|0|sp=us}} long, and was completed in 2000. {{coord|15|6|19.95|N|105|48|49.51|E|type:waterbody_region:LA|name=Pakxe}}).

The [[Kizuna bridge|Kizuna Bridge]] is in [[Cambodia]], in the city of [[Kampong Cham (city)|Kampong Cham]], on the road linking Phnom Penh with the remote provinces of [[Ratanakiri]] and [[Mondolkiri]], and Laos. The bridge opened for traffic on 11 December 2001.

The [[Prek Tamak Bridge]], {{cvt|40|km}} north of Phnom Penh opened in 2010.

Phnom Penh itself has no bridge under construction yet, although two new bridges have recently opened on the Tonle Sap, and the main bridge on the highway to Ho Chi Minh was duplicated in 2010.

[[Neak Loeung Bridge|Another new bridge]] was built at [[Neak Leung]] on the Phnom Penh to Ho Chi Minh [[National Highway 1 (Cambodia)|Highway 1]] with Japanese government assistance, and opened in 2015.

In [[Vietnam]], since the year 2000 [[Mỹ Thuận Bridge]] crosses the first channel—the left, main branch of the Mekong, the Sông Tiền or Tiền Giang—near [[Vĩnh Long]] and since 2008 [[Rạch Miễu Bridge]] crosses it near Mỹ Tho, between the provinces of Tiền Giang and Bến Tre.

[[Cần Thơ Bridge]] crosses the second channel—the right, main distributary of the Mekong, the Bassac (Song Hau). Inaugurated in 2010, it is the [[List of largest cable-stayed bridges|longest main span]] cable-stayed bridge in Southeast Asia.

==Environmental issues==
Drought linked to a changing climate and dozens of hydroelectric dams are damaging the Mekong ecosystem.<ref>{{cite news |last1=Sasipornkarn |first1=Emmy |title=A dam-building race threatens the Mekong River |url=https://www.dw.com/en/a-dam-building-race-threatens-the-mekong-river/a-50049206 |access-date=18 August 2019 |work=Deutsche Welle |date=16 August 2019}}</ref><ref>{{cite news |last1=Sripiachai |first1=Pattanapong |title=Mekong River falls to critical level, sand dunes emerge |url=https://www.bangkokpost.com/thailand/general/1782349/mekong-river-falls-to-critical-level-sand-dunes-emerge |access-date=26 November 2019 |work=Bangkok Post |date=29 October 2019}}</ref><ref>{{Cite news |last=Beech |first=Hannah |url=https://www.nytimes.com/2020/04/13/world/asia/china-mekong-drought.html |title=China Limited the Mekong's Flow. Other Countries Suffered a Drought. |date=13 April 2020 |work=The New York Times |access-date=14 April 2020 |language=en-US |issn=0362-4331}}</ref> When drought ends and the inevitable floods begin, the effects of Mekong dams on flood pulse dynamics over the entire Lower Mekong are poorly understood.<ref name="Pokhrel-2018">{{cite journal |last1=Pokhrel |first1=Yadu|display-authors=etal |title=Potential Disruption of Flood Dynamics in the Lower Mekong River Basin Due to Upstream Flow Regulation |journal=Scientific Reports |date=10 December 2018 |volume=8 |issue=17767 |page=17767 |doi=10.1038/s41598-018-35823-4 |pmid=30532063 |pmc=6288158 |bibcode=2018NatSR...817767P|doi-access=free}}</ref>

Sewage treatment is rudimentary in towns and urban areas throughout much of the Mekong's length, such as [[Vientiane]] in [[Water supply and sanitation in Laos|Laos]]. Water [[pollution]] impacts the river's ecological integrity as a result.{{Citation needed|date=February 2020}}

Much of the 8.3 billion [[tonne]]s of plastic present on earth<ref>{{cite news |last1=Franzen |first1=Harald |title=There are 8.3 billion tons of plastic in the world |url=http://www.dw.com/en/there-are-83-billion-tons-of-plastic-in-the-world/a-39765670 |access-date=17 April 2018 |work=Deutsche Welle |date=20 July 2017}}</ref> makes its way to the oceans. Ninety percent of plastic in the oceans is flushed there by just 10 rivers. The Mekong is one of them.<ref>{{cite news |last1=Franzen |first1=Harald |title=Almost all plastic in the ocean comes from just 10 rivers |url=http://www.dw.com/en/almost-all-plastic-in-the-ocean-comes-from-just-10-rivers/a-41581484 |access-date=17 April 2018 |work=Deutsche Welle |date=30 November 2017}}</ref>

A growing number of academics, NGOs, and scientists have urged the international community and the Mekong River Commission to reduce the use of hydropower, giving concerns of long-term sustainability. Some of them have urged an immediate moratorium on new construction of hydropower projects and a shift to solar and other forms of renewable energy, which are becoming more competitive and faster to install.<ref name=Yale-TF>{{cite web |last1=Fawthrop |first1=Tom |title=Dams and Climate Change Kill the Mekong |website=YaleGlobal Online |publisher=Yale University |date=28 November 2019 |url=https://yaleglobal.yale.edu/content/dams-and-climate-change-kill-mekong |access-date=26 November 2019}}</ref>

==See also==
{{portal|Rivers}}
{{div col|colwidth=20em}}
*[[Greater Mekong Subregion]]
*[[Greater Mekong Sub-region Academic and Research Network]]
*[[GMS Environment Operations Center]]
*[[Indochina]]
*[[Kong River|Sekong River]]
*[[Mekong River Basin Hydropower]]
*[[Mekong River massacre]] 2011 killings on Mekong river
*[[Stung Sen River]]
*[[Mekong Expedition of 1866-1868]]
*[[Fair river sharing]]
{{div col end}}
==References==
{{Reflist}}

==Further reading==
{{refbegin|40em}}
*{{cite book |editor1-last=Campbell |editor1-first=Ian  |title=The Mekong: biophysical environment of an international river basin |date=2009 |publisher=Academic Press |location=Amsterdam |isbn=978-0-12-374026-7 }}.
*{{cite book |author1-last=Cosslett |author-first=Tuyet L. |author2-last=Cosslett |author2-first=Patrick D.  |title=Sustainable Development of Rice and Water Resources in Mainland Southeast Asia and Mekong River Basin |date=2018 |publisher=Springer |location=Singapore |isbn=978-981-10-5613-0 }}
*{{cite book |author-last=Eyler |author-first=Brian  |title=Last days of the mighty Mekong |date=2015 |publisher=Zed Books |location=London |isbn=978-1-78-360720-4 }}.  
*{{cite book |editor1-last=Matthews |editor1-first=Nathanial |editor2-last=Geheb |editor2-first=Kim |title=Hydropower Development in the Mekong Region: Political, Socio-economic and Environmental Perspectives |date=2015 |publisher=Earthscan |location=London |isbn=978-1-315-86758-8 }}.
*{{Cite journal |author-last=Middleton |author-first=Carl |date=2016 |title=The Political Ecology of Large Hydropower Dams in the Mekong Basin: A Comprehensive Review |journal=Water Alternatives|language=en |volume=15 |issue=2 |pages=251–289 |url=https://www.water-alternatives.org/index.php/alldoc/articles/vol15/v15issue2/668-a15-2-10/file }}
*{{cite report |author=MRC  |title=State of the Basin Report 2018 |date=2019 |publisher=[[Mekong River Commission]] |location=Vientiane |issn=1728-3248 |url=http://www.mrcmekong.org/assets/Publications/SOBR-v8_Final-for-web.pdf }}.
*{{cite book |author-last=Osborne |author-first=Milton E.  |title=The Mekong: River Under Threat |date=2009 |publisher=Lowy Institute for International Policy |location=Double Bay |isbn=978-1-921004-38-4 }}.
*{{cite book |editor1-last=Renaud |editor1-first=Fabrice G. |editor2-last=Kuenzer |editor2-first=Claudia |title=The Mekong Delta System: Interdisciplinary Analyses of a River Delta |date=2012 |publisher=Springer |location=Dordrecht |isbn=978-94-007-3961-1 }}.
*{{cite book |editor1-last=Shoemaker |editor1-first=Bruce |editor2-last=Robichaud |editor2-first=William |title=Dead in the Water; Global Lessons from the World Bank's Model Hydropower Project in Laos |date=November 2019 |publisher=University of Wisconsin Press |location=Madison |isbn=9780299317942 |edition=Paper |url=https://uwpress.wisc.edu/books/5568.htm |access-date=26 November 2019}}
{{refend}}

==External links==
{{commons category|Mekong}}
{{GeoGroup}}
*[http://www.wisdom.eoc.dlr.de The WISDOM Project, a Water related Information System for the Mekong Delta]
*[http://www.mrcmekong.org Mekong River Commission]
*[https://wle-mekong.cgiar.org CGIAR Research Program on Water, Land and Ecosystems - Greater Mekong] {{Webarchive|url=https://web.archive.org/web/20210709185232/https://wle-mekong.cgiar.org/ |date=9 July 2021 }}
*[https://web.archive.org/web/20111114111257/http://www.mekongnet.org/ Mekong Watch]
*[http://www.adb.org/features/12-things-know-2012-greater-mekong-subregion-program Countries of the Mekong River: The Greater Mekong Subregion] Asian Development Bank
*[http://www.riversnetwork.org/rbo/index.php/river-blogs/south-asia/itemlist/category/14-mekong Rivers Network : Mekong river blog ] {{Webarchive|url=https://web.archive.org/web/20181105051137/http://www.riversnetwork.org/rbo/index.php/river-blogs/south-asia/itemlist/category/14-mekong |date=5 November 2018 }}
{{China Rivers}}
{{Cambodia rivers}}
{{Laos topics}}
{{Qinghai topics}}
{{Dams in the Mekong River Basin}}
{{Estuaries of the Mekong River}}
{{Authority control}}

[[Category:Mekong River| ]]
[[Category:Ecoregions of China]]
[[Category:Freshwater ecoregions]]
[[Category:International rivers of Asia]]
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[[Category:Isan]]
[[Category:Laos–Thailand border]]
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[[Category:Cambodia–Laos border]]
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[[Category:Lowest points of countries]]