The reservoir lies at a height of 900 feet (274 m), and measures some 12 acres (49,000 m2) in size.

The original dam was built in 1924 to provide hydro-electric power to the aluminium smelting works in Dolgarrog.

Water from the reservoir, which has a catchment area of around 27 square kilometres, is carried via a 3 km large metal pipe down to the hydro-electric power-station in Dolgarrog.

This excess water flows into a spectacular gorge used by outdoor pursuit groups.

Gorge walking here, however, can be dangerous because of the sudden releases of water from the reservoir which can occur.