Lough Allen is a lake on the River Shannon. Most of the lake is in County Leitrim, with a smaller part in County Roscommon. The lake and is the uppermost of the three main lakes on the river. The other two, Lough Ree and Lough Derg lying much further to the south.
The lake is shaped like an upturned isosceles triangle. The Shannon enters the lake at the wider northern end and leaves the lake at the narrow southern end. The Iron Mountains lie to the east and west of Lough Allen. (Read more)