Lough Neagh - United Kingdom

UK ECN site. Lough Neagh covers 383 km2 and is by far the largest area of freshwater in the British Isles. Situated in the north-east of the island, it has a drainage basin of 4,453 km2, which is shared between Northern Ireland (91%) and the Republic of Ireland (9%). The average water retention time is 15 months. Although large in area, the lake is relatively shallow with a mean depth of 8.9 m (max. 25 m). This, combined with its great size and a mild and windy oceanic climate, ensures that the water column is generally well mixed. The lake supports commercial fisheries for European eel, pollan, perch and trout. The eel fishery is the most significant, with an annual catch in the region of 600 t. Lough Neagh is hypertrophic with a mean annual total phosphorus (P) concentration of 140 mg P l-1 (2017). Levels of phosphorus and nitrogen in the lough support large phytoplankton populations with annual chlorophyll a concentrations typically in excess of 45 mg l-1. The dominant alga is the cyanophyte Planktothrix agardhii and the phytoplankton is now less diverse than in the late 1960s when regular monitoring began. Since then there has been regular monitoring of the plankton, lake and river nutrient concentrations, which have been used to produce nutrient budgets for the lake.