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The Upper Derwent Valley above Bamford is dominated by three large reservoirs, built between 1901 and 1945 to supply water to Sheffield, Nottingham, Derby and Leicester. Howden is the uppermost and oldest of the three; below that is Derwent Reservoir, filled between November 1914 and January 1916. Work on Ladybower Reservoir commenced in 1935 and, despite the shortage of materials and resources in the Second World War, was opened in 1945 by King George VI. Unlike the solid masonry dams built for the Howden and Derwent reservoirs, Ladybower Dam is a clay-cored earth embankment. Two villages were engulfed when Ladybower Reservoir was filled, Derwent and Ashopton, and their remains can still be seen when water levels are low. Famously, Derwent Reservoir was used by 617 Squadron in preparation for the ‘Dambusters’ raid on the dams of the Ruhr Valley in 1943.