A large Y-shaped reservoir, the lowest of three in the Upper Derwent Valley in Derbyshire.
Fed by the River Ashop from the west and the River Derwent from the north, flowing through
the Howden Reservoir, then the Derwent Reservoir, and finally through Ladybower Reservoir,
eventually feeding into the River Trent at Derby and thence to the Humber River and the North Sea.