Lough Neagh ( lokh NAY) is a freshwater lake in Northern Ireland and is the largest lake in the island of Ireland, the United Kingdom and the British Isles. It has a surface area of 151 square miles (392 square kilometres) and supplies 40% of Northern Ireland's water. Its main inflows come from the Upper River Bann and River Blackwater, and its main outflow is the Lower River Bann. Its name comes from Irish Loch nEachach [ˌl̪ˠɔx ˈn̠ʲahəx], meaning "Eachaidh's lake". The lough is owned by the Earl of Shaftesbury and managed by Lough Neagh Partnership Ltd.

Lough Neagh serves various recreational and commercial purposes. Traditional working boats and navigation routes were established for transport and trade, with only the Lower Bann remaining open today. The lough is also a popular destination for birdwatching, has diverse flora, and is known for its eel fishing industry. Lough Neagh Rescue, a voluntary service, provides search and rescue assistance around the lough.