This image was Taken at Howden Reservoir in the Derbyshire Peak District.

Howden reservoir is the first in a chain of 3 reservoirs proving water for the area. When rainwater and land drainage water fills this reservoir, it then overflows into the famous Derwent Reservoir where the Dambuster pilots practiced. When Derwent reservoir when full, it then overflows into Ladybower Reservoir.
These reservoirs are the main source of water for Severn Trent Water.