The River Blackwater (Irish: An Abhainn Mhór) or Ulster Blackwater is a river mainly in County Armagh and County Tyrone, Northern Ireland. Its source is to the north of Fivemiletown, County Tyrone. The river divides County Armagh from County Tyrone and also divides County Tyrone from County Monaghan, making it part of the border between the United Kingdom and the Republic of Ireland.
Lough Neagh (/lɒx ˈneɪ/ lokh NAY; Irish: Loch nEathach [l̪ˠɔx ˈn̠ʲaha(x)]) is a freshwater lake in Northern Ireland and is the largest lake on the island of Ireland and in the British Isles. It has a surface area of 148 square miles (383 square kilometres) and is about 19 miles (31 km) long and 9 miles (14 km) wide. According to Northern Ireland Water, it supplies 40.7% of Northern Ireland's drinking water.
Its main inflows are the Upper River Bann and Blackwater, and its main outflow is the Lower Bann. There are several small islands, including Ram's Island, Coney Island and Derrywarragh Island. The lake bed is owned by the 12th Earl of Shaftesbury and the lake is managed by Lough Neagh Partnership. Its name comes from Irish Loch nEachach [ˌl̪ˠɔx ˈn̠ʲahəx], meaning "Eachaidh's lake".