The reservoir lies in the parish of Grafton and collects rainfall from the eastern end of the Vale of Pewsey and the surrounding hills.

It was created by John Blackwell in 1836, by damming a narrow branching valley, and is fed by natural springs.

When the canal was built, there were no reliable water sources available to fill the summit by normal gravitational means.

However, a set of usable springs were found adjacent to the canal route about one mile (2 km) east of the summit pound, and about 40 feet (12 m) below it.

The reservoir outfall and sluices are designated as Grade II listed structures.