- Location: Mourne Mountains of south-eastern Northern Ireland
- Type: Lake
- Catchment area: 48 ha
- Annual rainfall: c. 1600 mm
- Lake area: 1.9 ha
- Lake altitude: 340 m
Blue Lough is situated in a col between the Silent Valley and Annalong Valley in the Mourne Mountains of south-eastern Northern Ireland, very close to Bencrom River. The catchment is small (48 ha), but is steep and rugged, reaching a maximum altitude of 703 m. The solid geology of the catchment consists of granite which is exposed as bare rock and scree on the steep backwall and is covered with thin and often eroded blanket peat, peaty podsols and peaty gleys in the less steep areas. Bare rock, scree and eroded peat characterise the catchment, but elsewhere the vegetation is dominated by Calluna which in places is mature and in others has been intensively burnt. Land-use and management is restricted to low-intensity sheep grazing and occasional heather burning.
Annual rainfall is c. 1600 mm.
Blue Lough is a small (1.9 ha) circular lake lying at 340 m altitude. The lough has no discrete inflow and drains through a Sphagnum bog to a tributary of the Annalong River. The bathymetry reveals a shallow concentric basin offset to the east, with a maximum depth of 5 m.
The site lies within the Eastern Mournes Area of Special Scientific Interest and Special Area of Conservation, as well as the Mourne Area of Outstanding Natural Beauty.
UK UWMN data from the site contributes to the UNECE International Cooperative Programme on Assessment and Monitoring of Acidification of Rivers and Lakes.