It was constructed by building a damming in the Gwash Valley, in 1975. It flooded most of Middle Hambleton. The remaining parts - now just named Hambleton are on a peninsular in the middle of the lake. It narrowly avoids flooding Normanton - the church of which was raised just in case.
It is not just used for storage of water, but is a popular sports centre - as well as water sports, there are fishing, walking and cycling, with a 25-mile perimeter track. A pleasure cruiser sails on the reservoir.
The reservoir is home to two nature reserves and the Anglian Water Bird Watching Centre. Every August, the centre is the venue for the British Birdwatching Fair.