It is a drinking water reservoir for Edinburgh and the Lothians and is located 320 metres (1,050 ft) above sea level.

[2] The reservoir is surrounded by the North Slipperfield Estate which manages the land for rough grazing and shooting.

[3] Erosion caused by the creation of the reservoir exposed an Early Bronze Age flat cist cemetery.

The reason for this is that in the autumn and winter the reservoir is host to a large roost of pink-footed geese which, in the years 2003–2008 had an average peak number of over 40,000 birds, almost 115 of the total population of this species.

Other important wintering and passage species include common goldeneye, barnacle goose, tufted duck and Eurasian teal.