Lough Derg (Shannon)

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Lough Derg (Shannon) is a freshwater lake in Ireland, part of the Shannon River system. It lies in three counties—Clare, Galway, and Tipperary—and is one of the island’s largest lakes. The name comes from the Irish Loch Deirgeirt, a form connected to the Dagda, a figure in Irish mythology.

The lake is long and narrow, about 38.6 km (24 miles) long and up to 12.9 km (8 miles) wide, covering about 130 square kilometers. It reaches depths of up to 36 meters (118 feet). Its shores host towns and villages such as Portumna, Killaloe & Ballina, Dromineer, Terryglass, Mountshannon, and Garrykennedy. Inis Cealtra, also known as Holy Island, lies on the lake.

Doonass Falls appear just downstream where Lough Derg flows into the Shannon. Nearby is the Ardnacrusha hydroelectric plant, built in 1927 and once the world’s largest hydroelectric station.

In the 19th century, Lough Derg was an important waterway for moving goods from Limerick to Dublin. Today it is popular for boating, sailing, and fishing. The University of Limerick runs an activity center by the lake north of Killaloe with canoes, windsurfing, and other water activities.

The lake hosts Ireland’s first inland RNLI lifeboat station, at Dromineer. In 2013, 35 people were rescued after severe weather affected a major rowing event.

There have been plans to use Lough Derg as a water source for Dublin. A 2011 plan proposed pumping up to 350 million litres of water a day from the lake, with a 2016 site choice at the Parteen Basin. Water would be moved to a storage tank near Cloughjordan and then gravity-fed to Dublin.

Wildlife and conservation notes include a white-tailed eagle pair nesting on an island in 2012, a record of the invasive alga Nitellopsis obtusa in 2016, and the discovery of invasive quagga mussels in 2021 in Lough Derg and nearby Lough Ree. The North-East Shore of the lake is designated as a Special Area of Conservation.