It has been proposed that the reservoir be designated as a local nature reserve to be managed by West Lothian Council.

[1] Harperrig reservoir lies in the middle of a basin on the northwestern side of the Pentland Hills some 19 kilometres (12 miles) from south west of Edinburgh.

The reservoir holds 4,091,481 m3 (900,000,000 imp gal) of water[1] and has a surface area of 94.4 hectares (233 acres).

The ruin of Cairns Castle, dating from around 1440 and built by George Crichton, is situated on a hillock which projects into the reservoir.

Both boat and bank fishing are allowed and the reservoir is stocked with brown trout.