From Wiki Howden Reservoir is a Y-shaped reservoir, top one of the three in the Upper Derwent Valley, England. The western half of the reservoir lies in Derbyshire, whereas the eastern half is in Sheffield, South Yorkshire. The county border runs through the middle of the reservoir, following the original path of the River Derwent. Work commenced on the dam's construction on 16 July 1901 and completed in July 1912. The chief engineer was Mr Edward Sandeman. The dam is of solid masonry construction, and 117 ft tall (36 m), 1,080 ft long (330 m), and impounds 1,900,000 imperial gallons (8,600 kl) of water, from a catchment area of 5,155 acres (20.86 km2).