River Shannon

River Shannon
River Shannon from Drumsna bridge, County Leitrim
River Shannon watershed (Interactive map)
Native name	Abhainn na Sionainne (Irish)
Location
Country	Ireland
Counties	Cavan, Leitrim, Longford, Roscommon, Westmeath, Offaly, Tipperary, Galway, Clare, Limerick, Kerry
Physical characteristics
Source	Shannon Pot
• location	Glangevlin, Cuilcagh Mountain, County Cavan
• coordinates	54°14′06″N 7°55′12″W / 54.235°N 7.92°W / 54.235; -7.92
• elevation	100
Mouth	Shannon Estuary
• location	Limerick
• coordinates	52°39′25″N 8°39′36″W / 52.657°N 8.66°W / 52.657; -8.66
Length	360 kilometres (220 mi)
Discharge
• maximum	300 cubic metres per second (11,000 cu ft/s)

The River Shannon (Irish: Abhainn na Sionainne, an tSionainn, an tSionna) is the major river on the island of Ireland, and at 360 km (224 miles) in length,^[1] is the longest river in the British Isles.^[2][3] It drains the Shannon River Basin, which has an area of 16,900 km² (6,525 sq mi),^[4] – approximately one fifth of the area of Ireland.

Known as an important waterway since antiquity, the Shannon first appeared in maps by the Graeco-Egyptian geographer Ptolemy (c. 100 – c. 170 AD). The river flows generally southwards from the Shannon Pot in County Cavan before turning west and emptying into the Atlantic Ocean through the 102.1 km (63.4 mi) long Shannon Estuary.^[5] Limerick city stands at the point where the river water meets the sea water of the estuary. The Shannon is tidal east of Limerick as far as the base of the Ardnacrusha dam.^[6] The Shannon divides the west of Ireland (principally the province of Connacht) from the east and south (Leinster and most of Munster; County Clare, being west of the Shannon but part of the province of Munster, is the major exception.) The river represents a major physical barrier between east and west, with fewer than thirty-five crossing points between the village of Dowra in the north and Limerick city in the south.