Erne (ûrn) [key], river, 72 mi (116 km) long, rising in Lough Gowna, Co. Longford, N Republic of Ireland. It flows NW through SW Northern Ireland, then back through the Republic before entering the Atlantic Ocean at Donegal Bay. Grazing predominates in the Erne basin; Enniskillen is the chief town. In Northern Ireland the river expands to form two large lakes—Upper Lough Erne (10 mi/16.1 km long) and Lower Lough Erne (18 mi/29 km long). An international flood-control scheme (completed 1959) controls the water level in the lakes. Hydroelectricity is produced along the 150-ft (46-m) drop in the river's course between Belleek and Ballyshannon; the lakes are a natural reservoir.