Shannon River Basin
The Shannon River Basin consists of the area containing Ireland's longest river, the River Shannon, and all of its tributaries and lakes. The official Ordnance Survey Ireland length of the Shannon from its Shannon Pot source is 224 miles (360 km) made up of 63.5 miles (102.2 km) tidal water flow and 160.5 miles (258.3 km) freshwater flow.
It has a Long Term Average Flow of 208.1 m3/s (7,350 cu ft/s) (at Limerick City). This is double the flow rate of Ireland's second largest river, the River Corrib (104.8 m3/s [3,700 cu ft/s]). If the discharges from all of the rivers and streams into the Shannon Estuary (including the rivers Feale 34.6 m3/s, Maigue 15.6 m3/s, Fergus 25.7 m3/s, and Deel 7.4 m3/s) are added to the discharge at Limerick, the total discharge of the River Shannon at its mouth at Loop Head reaches 300 m3/s (11,000 cu ft/s).
The River Shannon is a traditional freshwater river for just 45% of its total length. Excluding the 63.5-mile (102.2 km) tidal estuary from its total length of 224 miles (360 km), if one also excludes the lakes (L. Derg 24 mi, L. Ree 18 mi, L. Allen 7 mi plus L. Boderg, L. Bofin, L. Forbes, L. Corry) from the Shannon's freshwater flow of 160.5 miles (258.3 km), the Shannon as a freshwater river is only about 100 miles (160 km) long.
The Shannon River Basin is part of the Shannon International River Basin District (SHIRBD) administrative area which has an area of 17,963 km2 (6,936 sq mi) in area. In addition to the Shannon Basin, the district also covers coastal parts of Kerry and Clare which drain to the sea. The SHIRBD contains 7,666 km (4,763 mi) of rivers, 1,220 km (760 mi) of coastline including estuaries, and 113 lakes, including 53 over 50 hectares (120 acres) in size. The main land use throughout the SHIRBD area is agriculture (70.7%). Peatlands (11.1%) and forestry (3.2%) are also important. The SHIRBD's population is 618,884 at 34 inhabitants per square kilometre (88/sq mi) (Census data 2002).
There are some tributaries within the River Shannon system which have headwaters that are further in length (from source to mouth) than the Shannon Pot source, such as the Owenmore River in County Cavan, which flows west for 14.5 km (9.0 mi) through the valley of Glangevlin before joining the Shannon about 3 km (2 mi) below the Shannon Pot at Lugnashinna, thus adding 11 km (7 mi) to the Shannon's overall length, bringing it to 372 km (231 mi).
Also the Boyle River has a similar claim. The river flow from the furthest reaches of the Boyle catchment to Limerick city has a measurement of 290 km (180 mi). When added to the Shannon's 102.2 km (63.5 mi) estuary this gives a total river flow of 392.1 km (243.6 mi), which makes it the longest river within the River Shannon basin (from source to mouth)—31.6 km (19.6 mi) longer than the Shannon Pot source. Thus the Boyle-Shannon river can be regarded as having the longest natural river flow in Ireland.
The River Shannon Basin touches more than half (17) of Ireland's counties:- Limerick, Clare, Tipperary, Offaly, Westmeath, Longford, Roscommon, Kerry, Galway, Leitrim, Cavan, Sligo, Mayo, Cork, Laois, Meath and Fermanagh.
There are many towns situated in the Shannon Basin.
Towns and Villages (with 2011 populations) within the Shannon River Basin and the rivers and riverbanks on which they stand:
Shannon River: (going downstream)
- Drumshanbo (Lough Allen Canal - Left Bank) 857
- Leitrim Village (L. Bank) 485
- Carrick-on-Shannon 3,980
- Jamestown (L. Bank)
- Drumsna (L. Bank) 247
- Drumod (Lough Boderg - L. Bank) 356
- Roosky (Right Bank) 188
- Termonbarry (R. Bank) 366
- Cloondara (L. Bank)
- Lanesborough 1,388
- Athlone 20,153
- Clonmacnoise (L. Bank)
- Shannonbridge (L. Bank) 206
- Banagher (L. Bank) 1,653
- Portumna (R. Bank) 1,530
- Terryglass (Lough Derg - L. Bank)
- Mountshannon (Lough Derg - R. Bank) 152
- Dromineer (Lough Derg - L. Bank) 113
- Ballina (L. Bank) 2,442
- Killaloe (R. Bank) 1,292
- O'Briensbridge 235
- Castleconnell (L. Bank) 1,917
- Limerick City 87,081
- Shannon (S. Estuary - R. Bank) 9,673
- Kilrush (S. Estuary - R. Bank) 2,695
- Carrigaholt (S. Estuary - R. Bank)
- Foynes (S. Estuary - L. Bank) 543
- Glin (S. Estuary - L. Bank) 577
- Tarbert (S. Estuary - L. Bank) 551
- Ballylongford (S. Estuary - L. Bank) 418
- Ballybunion (S. Estuary - L. Bank) 1,354
Shannon River tributaries:
- Boyle river: Boyle 2,588
- Lung river: Ballaghaderreen (outskirts) 1,822
- Camlin river: Longford 9,601
- Hind river: Roscommon (outskirts) 5,693
- River Inny (Leinster): Mullingar 20,103
- River Brosna: Ballymahon 1,563, Ferbane 1,165, Tullamore (Tullamore river) 14,361
- River Suck: Castlerea 1,985, Athleague 241, Ballinasloe 6,577
- Little Brosna river: Birr 5,452
- Ballyfinboy River: Borrisokane 1,145, Cloughjordan 511
- Nenagh river: Nenagh 8,439
- River Graney: Scariff 798
- Bunratty river: Sixmilebridge 1,839, Bunratty 219
- River Fergus: Ennis 25,360, Newmarket-on-Fergus 1,773
- River Maigue: Adare 1,106
- River Deel: Rathkeale 1,550, Askeaton 1,149
- River Feale: Listowel 4,338, Abbeyfeale 2,007
Tributary Sub Catchments
Freshwater Catchments (With Areas - km2) Going downstream
- L Allen (upstream from L. Allen outlet) 415 km2
- Eslin River 73 km2
- River Rinn 311 km2
- Camlin River 352 km2
- River Inny (Leinster) 1,254 km2
- River Brosna 1,248 km2
- Little Brosna River 662 km2
- Ballyfinboy River 182 km2
- Nenagh River 321 km2
- Mulkear River 660 km2
- Boyle River 725 km2
- Hind River 78 km2
- River Suck 1,600 km2
- Cappagh/Kilcrow 414 km2
- River Graney 295 km2
Estuarine Catchments Areas
There are many other smaller tributaries which join the Shannon along its journey.
There are a multitude of lakes within the Shannon River Basin, both on the main river and throughout the sub-catchments.
Here is a table showing the major lakes:
|Lough Derg||130 km2||Shannon|
|Lough Ree||105 km2||Shannon|
|Lough Allen||35 km2||Shannon|
|Lough Sheelin||19 km2||Inny|
|Lough Ennell||14.34 km2||Brosna|
|Lough Gara||11.9 km2||Boyle|
|Lough Derravaragh||10.8 km2||Inny|
|Lough Owel||10.3 km2||Brosna|
|Lough Bofin/Boderg/Scannal||9.7 km2||Shannon|
|Lough Key||8.4 km2||Boyle|
|Lough Graney||3.7 km2||Graney|
|Lough Forbes||3 km2||Shannon|
|Lough Eidin (Drumharlow Lough)||2.7 km2||Boyle|
|Lough Funshinagh||2.5 km2||Shannon|
- Ordnance Survey (Ireland) Educational Facts
- Biology and Management of European Eel (Anguilla anguilla, L) in the Shannon Estuary, Ireland 
- South Eastern River Basin Management: Page 38 Archived 2016-03-03 at the Wayback Machine.
- Long-term effects of hydropower installations and associated river regulation on River Shannon eel populations: mitigation and management 
- SFPC Maintenance Dredging Application: Table 3-7 Archived 2014-12-08 at the Wayback Machine.
- Ask about Ireland
- "Shannon River Basin District". Archived from the original on 2016-04-14. Retrieved 2018-05-08.
- Shannon International River Basin District Eel Management Plan Archived 2013-12-14 at the Wayback Machine.
- Ordnance Survey of Ireland: Rivers and their Catchment Basins 1958 (Table of Reference)
- P. W. Joyce (1900). "Cavan". Atlas and Cyclopedia of Ireland. Murphy & McCarthy.
- River Habitat Survey, Fig. 2
- European Commission Rivers Map
- Shannon Catchment-based Flood Risk Assessment and Management (CFRAM) Study. Page 3 
- Census 2011 – Population Classified by Area - Table 5
- Dublin Marine Institute 1998: Studies of Irish Rivers and Lakes: Moriarty, Christopher - Table 10.1.
- Google Maps
- THE GSI GROUNDWATER NEWSLETTER - Page 9