Planned by the Fylde Water Works in 1860 as part of a scheme to supply Blackpool and the Fylde Coast with water, this was the third, final and largest reservoir to be built. At the time of its completion, the total capacity of Grizedale, Barnacre and Grizedale Lea Reservoirs was over half a billion litres (128.8 million gallons).
The photograph hasn't quite captured the surprisingly colourful 'tidemarks' on the gravel banks.
Grizedale Fell is in the background, in the Forest of Bowland AONB.