The 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. The longest arm is around 1.25 miles (2 km) in length. The reservoir is bounded at the southern end by Howden Dam; below this, the River Derwent flows immediately into Derwent Reservoir and subsequently the Ladybower Reservoir.