The River Erne ( or An Éirne), in the northwest of Ireland, is the second-longest river in Ulster. It rises on the east shoulder of Slieve Glah mountain three miles south of Cavan in County Cavan and flows 80 miles (129km) through Lough Gowna, Lough Oughter and Upper and Lower Lough Erne, County Fermanagh, to the sea at Ballyshannon, County Donegal. For 30 miles from Crossdoney in County Cavan to Enniskillen in County Fermanagh, it is difficult to distinguish the river as it winds its way through interconnected loughs or parts of loughs nestling among the drumlin hills of Cavan and south Fermanagh. The river is 120 kilometres long and is very popular for fly fishing for trout and salmon, with a number of fisheries along both the river itself and its tributaries. The town of Enniskillen is mostly situated on an island in the river, between Upper and Lower Lough Erne. It is linked to the River Shannon by the Shannon–Erne Waterway. The total catchment area of the River Erne is 4,372 km². The long-term average flow rate of the River Erne is 101.7 cubic metres per second (m³/s)