Lough Mask: The Lake That Drains Underground

Lough Mask is a limestone lake of about 83 square kilometres, the sixth largest on the island of Ireland and the fourth largest in the Republic in Ireland by area, and with 1.3 cubic kilometres of water it holds more than any other lake in the Republic. It is the middle one of three lakes: Lough Carra drains into it through the Keel River, and it drains south into Lough Corrib — partly through the Cong Canal and partly through underground passages in the limestone, which come together at Cong to form the River Cong. The canal was meant to make that link navigable, as part of a drainage and navigation scheme part-funded by the Treasury in the Famine years, and it was abandoned unfinished in 1854, which is why it is known as the Dry Canal. The eastern half of Mask is shallow and full of islands; the western half sinks to a trench more than 50 metres deep.