The largest area of fresh water in the British Isles. Lough Neagh, is an eutrophic lake 385 km2 in area, mean depth 8.9 m, and is located centrally in the province of Northern Ireland. The lake is so shallow that the water remains always muddy due to wave and turbulent mixing by strong winds. The lake does not stratify in summer and very rarely freezes in winter. Transparency varies between 1.0-2.0 m due to the brown water and large phytoplankton crops which are dominated by blue-green algae and diatoms. It is an important eel and salmon fishery, provides the main water supply for the city of Belfast and the lake-bed is worked for sand and gravel (Q, 10).