Tonlé Sap

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Tonlé sap
NASA satellite image
Coordinates 12°53′N 104°04′E / 12.883°N 104.067°E / 12.883; 104.067Coordinates: 12°53′N 104°04′E / 12.883°N 104.067°E / 12.883; 104.067
Primary outflows Tonle sap River
Basin countries Cambodia
Surface area 2,700 km2 (1,000 sq mi) (normal)
16,000 km2 (6,200 sq mi) (monsoon)

The Tonlé sap (Khmer: ទន្លេសាប IPA: [tunleː saːp], "Large Fresh water River", but more commonly translated as "Great Lake") is a combined lake and river system of major importance to Cambodia.

The Tonlé sap is the largest freshwater lake in Southeast Asia and is an ecological hot spot that was designated as a UNESCO biosphere in 1997.[1]

The Tonlé sap is unusual for two reasons: its flow changes direction twice a year, and the portion that forms the lake expands and shrinks dramatically with the seasons. From November to May, Cambodia's dry season, the Tonlé sap drains into the Mekong River at Phnom Penh. However, when the year's heavy rains begin in June, the Tonlé sap backs up to form an enormous lake.

Tonle Sap inhabitants


Tonle Sap stilt houses

The Tonlé sap Lake is linked to the sea via the Tonlé sap River, which converges with the massive Mekong River in Phnom Penh. water has always been an important resource for Cambodia, as it is the origin of its creation.[2] According to legend, the Khmer people were colonized in the first centuries by peaceful neighbors from India, and the combination of the two cultures eventually formed the kingdom of Cambodia. Researches have found drawings of fish etched on temple walls in such elaborate details that they could be classified as well as etchings of men with nets.[3] To further highlight the importance of water, Cambodia’s capital city, Phnom Penh, was built at the convergence of the Tonlé sap River and the Mekong River. Still today, the harbor resembles the descriptions recorded by first explorers, and a boat adventure from Phnom Penh is reported to be the best way to explore the river and experience Cambodian culture.[2]

Volume and flow reversal[edit]

For most of the year the lake is fairly small—around one metre deep and with an area of 2,700 square kilometres (1,000 sq mi). When water is pushed up from the Mekong into the lake, it increases its area to approximately 16,000 square kilometres (6,200 sq mi), with a depth of nine meters. This expansion floods the nearby fields and forests, providing a great breeding ground for fish.[4]

Map of Tonle sap Lake and its floodplain

Along with seasonal expansion and shrinking of the river, the Tonlé sap is also unusual for its biannual flow reversal. The river reaches maximum flow in August and September, when the Mekong River swells massively as it collects melted water from the Himalayas as well as heavy monsoon rains in its upstream drainage basin which spans five countries. Coverging with the Tonlé sap in the Cambodian capital, the volume surge reverses much of the flow back up into the Tonlé sap floodplain. At the start of the dry season, the Mekong River water levels drop, returning the Tonlé sap River flow to its usual seaward direction, exposing the muddy lake plain.[5] May to October is wet season in Cambodia, bringing 75% of Cambodia’s rainfall. Dry season is from October to April.[citation needed]

Celebration of the Seven-Headed snake[edit]

This celebration also goes by the name Water and Moon Festival and was established to mark the reversal of the Tonlé sap and open the fishing season. The festival lasts three days and begins on the last day of the full moon. However, because of the variation of the monsoon seasons, the reversal of the river does not always coincide exactly with the festival. In the simplest form, the celebration is a series of canoe races, including some 375 teams, and victory brings good fortune for the coming fishing season for the entire village. In addition, these water celebrations are a tribute to one of the Buddhist teeth that Naga, whose daughter married an Indian prince to establish the kingdom of Cambodia, lost in the depths. According to legend, when he was cremated, his tooth fell into the river down to the seven-headed snakes kingdom.

In pagodas along the river, men prepare for the festival by either restoring sacred canoes that have existed for hundreds of years or building new canoes when the old ones are beyond repair. Canoes are made from one piece of a trunk of a coki tree; the wood of the coki tree is resistant to rotting. Each canoe is painted with patterns and eyes that symbolize the guardian goddess, often the spirit of a young tillage girl. This is a modification from the superstitious tradition of sacrifice of nailing actual eyes to the boat, dating back before Buddhism. The morning after completion and after three sacred shouts by the crew, the canoes are pushed into the river and head for the capital at full moon. Some crews must row for hours, and others will row for several days. Being chosen as a member of the crew is one of a man’s highest honors, and members must practice to perfect team coordination. Only the best crews will get to the finals in the capital.

After two days of racing, all of the canoes come together to encourage Naga to spit out the swelling waters of the Tonlé sap towards the sea. Firecrackers light the water, the royal palace, and the sky. This moment lets the legendary snake master of water know to return to the depths of the Tonlé sap and leave the power to the sun gods. This also marks the end of the rainy season.[2]

Fishing industry[edit]

When the Tonlé sap floods, the surrounding areas become a prime breeding ground for fish. During this time, fishermen are scarce; fishing during this time is actually illegal, so as to prevent disruption of mating. At the end of the rainy season, when the water levels go down, fishing is allowed again. Fishermen install floating houses along one half of the river, and the other half is left open for navigation.

Most of the fishing captains are of Vietnamese origin, and they primarily supply the country’s markets. Fisherman Sakaloy explains, “My parents were fishermen. We have lived in Cambodia and have this activity for a long time. We started well before the Pol Pot era, when the Khmer Rouge took over from 1975 to 1979. We had to flee to Vietnam, [but] afterwards we came back and have been fishing on the Tonlé sap ever since.” However, thousands of peasants follow this lifestyle hoping for an incredible catch, making it difficult to find spaces big enough to settle with all of the village carts.[2]

Fishing on Tonle Sap

The process of actually catching fish is simple, but the aftermath takes much more time and effort. Because of the drop in the water level, the Tonlé sap naturally carries away thousands of fish. The fishermen simply place cone-shaped nets into the water from their floating houses and then lift the net as soon as seconds later. Using this technique, two or three tons of fish are trapped each time and more than ten thousand tons of fish can be caught in under a week. One by one, fishermen, mostly women, cut off the fish heads then bring the fish back to the river to be cleaned and to remove the fat. Salting the fish for preservation is the final step in this process, but the fish will continue to macerate for several months in order to transform into a paste called prahok, a nourishing condiment that complements almost any dish. These couple of days, on average three days, of fishing supply enough prahok for the entire year.[6]

A vendor grilling fish at a local market

Fishermen use all parts of the fish for their own needs and also for profit. The removed heads of the fish are dried in the sun, becoming a good fertilizer they can sell. This small amount of extra money is acquired for cases of emergency, such as family illness. By boiling the fat from the bottom of the fish basket, fishermen can also make soap for their personal use. Through bartering on the banks, they exchange fish for rice. Excess rice is also sold for profit. Despite paying employees and buying an official fishing license, fishermen still “have enough money to feed my family for a year. So I don’t need rice fields.” To further emphasize the importance of fish in the local economy, the name given to the Cambodian form of currency is Riel, which is a small silver carp that is the staple of most diets.

The implication of the fishing industry in Cambodia is the country’s strong connection to religion, specifically Buddhism. Because of the moral consequences of taking a life, Buddhists limit Cambodian fishing to the amount necessary to feed their families. Additionally, to further lessen the guilt, fishermen do not actually kill the fish; instead they wait for it to die naturally when taken out of the water. Even so, fishermen go to pagodas after the fishing season for purification.[2]

Rice industry[edit]

The beginning of the dry season is also the beginning of rice season, which is the only source of wealth for peasants. A good harvest will provide enough rice for them to survive for the entire year, but if the floods are too big or too small, rice can become scarce. Because of this uncontrollable instability, many celebrations are held in honor of gods and genies that can influence nature and bring about a good harvest.

Tonle sap rice fields

Historical research has shown that the old Angkorian civilization took advantage of the weather conditions by digging huge reservoirs during the wet season and releasing the water during the dry season using an irrigation system and the land’s natural slope. This double and sometimes even tripled the amount of rice crops per year, strengthening the developing nation. However, today, this irrigation network is no longer present, and peasants only get one rice crop a year. What has not changed is the planting of rice in fields as well as the survival value of rice. It is still the main source of income for peasants and the only currency used to bargain. They use the crops to pay for what they need, such as property rent for land to plant, and the rest is kept for the family to eat.

A villager harvesting rice

In the fields villagers harvest and thresh traditionally, no machinery is used. As the sun rises, they reap the mature rice plants and replant new ones in their place. Harvested rice plants are cleaned, sprayed, and bundled. Women stoop for hours, their feet in the mud, to replant each rice root, and as the water recedes, a field of green is once again visible. Part of the rice harvest is grilled, ground, and winnowed, a ritual preparation for the upcoming celebration. Rice is also used to prepare lunch. One meal reflective of both the fishing and rice industry is Tonlé sap chicken. The rice and chicken is cooked in the river’s water, and prahok paste made from fish, is then mixed in to add flavor.

At the end of the rice season, villagers celebrate by marching in a procession to the pagoda. This is a chance for everyone to relax after the long labor of the harvest season. As well, it provides an opportunity to have fun and bond with the community. All the villagers wear their nicest clothes, musicians sing and dance, and men take the opportunity to court young women. Upon arrival, believers circle the temple three times and then proceed to present gifts such as clothing, dishes, furniture, and food. These donations, named Kathen by Buddha, provide help for bonzis, who in turn give blessings. This act of donation is essential in accumulating good karma for reincarnation, so eventually to reach Nirvana, or ultimate salvation, as well as for future harvests.[2]


Although the large amount of sediment in the Tonlé sap Lake basin is a natural phenomenon, rapid rates of development and resource exploitation has caught the attention of observers who fear the basin itself is in danger of filling with sediment. These fears were first reported by local people living lakeside that noticed some areas becoming shallower. With increased sedimentation, already vague transit routes between capital and regional centers would likely be shut down altogether and may restrict the migration of fish into the lake.

Because sediment contains nutrients that fuel food webs, the Tonlé sap is actually benefitting from the influx. Sediment-bound phosphorus serves as food for phytoplankton through higher plants, and research has shown that the metabolizing of the chemical contributes to food abundance and quality. Internal nutrient cycling, therefore, plays an essential role in productivity of a floodplain.[7] The nutrients bound to suspended sediments are important for the Tonle sap system, particularly to maintain its long-term sustainability.[8]

The reversal of the Tonlé sap river's flow also acts as a safety valve to prevent flooding further downstream. During the dry season (December to April) the Tonlé sap Lake provides around 50% of the flow to the Mekong Delta in Vietnam.

The lake occupies a depression created due to the geological stress induced by the collision of the Indian subcontinent with Asia. In recent years, there have been concerns from scientists about the building of high dams and other changed hydrological parameters in southern China and Laos that has threatened the strength and volume of the reverse flow into Tonle sap, which in turn decreases nesting, breeding, spawning, and feeding habitats in floodplain, which results in adverse impacts on fish productivity and overall biodiversity.[9]

Species diversity[edit]

Crocodile farm near Tonle sap
Spot-billed pelican
Mekong giant catfish

The river is home to at least 149 species of fish, eleven globally threatened species, and six near-threatened species. These species include the spot-billed pelican, greater adjutant, Bengal florican, darter, grey-headed fish eagle, and the Manchurian reed warbler. Specifically, the large colonies of unique birds constitute the Preak Toal Bird sanctuary. In addition, the Tonlé sap also supports significant reptile populations including nearly extinct Siamese crocodiles and the world’s largest population of freshwater snakes. Although the area around the lake has been modified for settlement and farming, about 200 species of plants have been recorded.[10]

One of the most legendary species living in the Tonlé sap is the Mekong giant catfish, one of the largest freshwater fish in the world. The fish is 2.4 to 3.0 metres (8 to 10 ft) long and can weigh anywhere between 110 and 230 kilograms (250 and 500 lb). The largest of these catfish ever caught weighed 306 kilograms (674 lb). Despite its massive physical characteristics, the Mekong catfish is especially vulnerable to chemical changes, which is beneficial in alerting authorities of trouble in the river ecosystem early on. The population of these fish has been steadily declining since the Khmer Rouge era, led by Pol Pot, and in 2005, fisherman reported that on average only one giant catfish was caught per day. Currently, it is illegal for fishermen to catch and keep these fish with the exception of a few retained by fisheries for research. It also cannot be used in any form of trade in fear of the economic exploitation.[11]

Biosphere reserve[edit]

In 1997, the United Nations Educational, Scientific and Cultural Organization, more commonly known as UNESCO, deemed Tonlé sap an ecological hotspot. As a result, in 2001, by royal Decree issued by the government of Cambodia, the lake and its surrounding provinces became the Tonle sap Biosphere Reserve. There are nine provinces that are part of the Tonle sap Biosphere Reserve. These are Banteay Meanchey, Battambang, Kampong Chhnang, Kampong Thom, Preah Vihear, Pursat, Siem Reap, Otdar Meanchey and Pailin.

The government is responsible for fulfilling three functions:

a) a conservation function to contribute to the conservation of biological diversity, landscapes, and ecosystem, including genetic resources, plant, fishery and animal species, and to the restoration of the essential character of the environment and habitat of biodiversity;

b) a development function to foster sustainable development of ecology, environment, economy, society, and culture;

c) a logistic function to provide support for demonstration projects, environmental education and training, research and monitoring of environment related to the local, national and global issues of conservation and sustainable development.

Additionally, the Tonlé sap Biosphere Reserve established three zones: a core zone, a buffer zone, and a transition zone. Formally, the core area of a Biosphere Reserve is defined as an area devoted to biological resources, landscapes, and ecosystems. The core zone includes practices that protect sites for conserving biodiversity, monitoring minimally disturbed ecosystems and undertaking non-destructive research and related activities. As of today, the three zones are Prek Toal, Boeng Chhmar, and Stung Sen.

Despite this government protection, illegal fishing, poaching, and cutting of the forest for farmland are all still major problems. Because people living around the lake are extremely poor and depend on the lake for their survival, it is likely that this unsustainable living will continue. During recent years, the amount of fish caught has been steadily declining, which means peasants must also work harder to provide for their families. The government is working on supporting and educating these people to break this cycle of poverty and unsustainability. Finding a balance between survival and conservation seems to be the major question for the future.[12]

People and culture[edit]

Floating basketball court on Tonle Sap
Floating church on Tonle Sap

The area is home to many ethnic Vietnamese and numerous Cham communities, living in floating villages around the lake. Approximately 1.2 million people living in the greater Tonle sap make their living by fishing on the local waters. Cambodia produces about 400,000 tonnes of freshwater fish per year, the majority of which comes from Tonle sap. These fisheries account for 16 percent of national GDP, making the fish industry not only essential to the diet of local populations but to the Cambodian economy as a whole.[13]


The boat from Phnom Penh to Siem Reap

Boats connect Phnom Penh to Siem Reap and usually take 6-7 hr and cost US$35.


  1. ^ Conservation Project of the Century, Miami Herald July 13, 1997 [1]
  2. ^ a b c d e f Children of the Seven-Headed snake. Dir. Didier Fassio. Perf. Didier Fassio. Film Makers Library, 2002. Film.
  3. ^ Hall, Kenneth (1985). Maritime trade and state development in early Southeast Asia. Honolulu: University of Hawaii Press. ISBN 0824809599. 
  4. ^ Busshoff, Dagmar. "A River Runs Through It: Cambodia's Splashy Bonn Om Touk Festival". Retrieved 2013-04-25. 
  5. ^ Marshall cavendish Corporation (2007). World and Its Peoples: Cambodia, Laos, and Vietnam. Marshall cavendish. pp. 727–. ISBN 978-0-7614-7639-9. 
  6. ^ Regional Office for Asia and Pacific. "Tonle Sap Fisheries". Retrieved 2013-04-30. 
  7. ^ Kummu, Matti; Dan Penny; Juha Sarkkula; Jorma Koponen (May 2008). "Sediment: Curse or Blessing for Tonle Sap Lake?". Royal Swedish Academy of Sciences 37 (3): 158–162. 
  8. ^ Sediment: Curse or Blessing for Tonle Sap Lake?
  9. ^ Impacts on the Tonle Sap Ecosystem, Probe International
  10. ^ Campbell, Ian; Colin Poole; Wim Giesen; John Valbo-Jorgensen (2006). "Species diversity and ecology of Tonle Sap Great Lake, Cambodia". Aquatic Sciences 68: 355–370. 
  11. ^ Sullivan, Michael (12/07/05). "Tonle Sap: The Flowing Heart of Cambodia". NPR. Retrieved 2013-04-20.  Check date values in: |date= (help)
  12. ^ Wildlife Conservation Society. "The Tonle Sap Biosphere Reserve". Retrieved 2013-04-20. 
  13. ^ Nicolaas Van Zalinge, Data Requirements for Fisheries Management in the Tonle Sap, MRC Fisheries Program

Further reading[edit]

  • Kuenzer, C., 2013, field Note: Threatening Tonle sap: Challenges for Southeast-Asia´s largest Freshwater Lake, The Pacific Geographies (PG), ISSN 2196-1468, pp. 29–31
  • Milton Osborne, The Mekong, Turbulent Past, Uncertain Future (Atlantic Monthly Press, 2000) ISBN 0-87113-806-9

External links[edit]