Fed by the Little Don or Porter River, it is around a mile long, and supplies water for Sheffield and Barnsley via the Langsett Treatment Works.

Construction of the reservoir began in 1898, the logistics of getting the workforce and materials to Langsett caused great difficulty as most of them came up from Sheffield.

[1] The minor road (Midhope Cliff Lane) which runs across the embankment is thought to be the longest single carriageway of any reservoir in Great Britain.

Gainsford closed the valve in the Langsett tower and the reservoir started to fill up, he was then presented with a golden key by the engineer William Watts.

In 2007 a pond was created near Brookhouse Bridge at the western end of the reservoir to help dragonflies, frogs, newts and toads establish new colonies.

South Yorkshire Water Authority gave permission in December 1981 to build the works in an old quarry adjacent to the reservoir wall.