Shannon, River, is the longest river and chief waterway of the Republic of Ireland. It rises in the Cuilcagh Mountains of northwestern Ireland and flows southwest about 230 miles (370 kilometers) to the Atlantic Ocean. Three major loughs (lakes)—Allen, Ree, and Derg—lie along its course. At Limerick, about 70 miles (110 kilometers) from the Atlantic, the river widens into a long estuary (coastal river mouth). There are ports at Limerick and Foynes on the estuary, which experiences ocean tides. The river is a popular site for pleasure cruising. Ireland’s largest river hydroelectric plant was built on the Shannon between Lough Derg and Limerick in the 1920’s. The Grand and Royal canals, built in the late 1700’s and early 1800’s, link the river with Dublin, on Ireland’s east coast. 
