The Hengsteysee (Lake Hengstey) is a reservoir on the Ruhr river between the cities of Hagen, Dortmund and Herdecke, North Rhine-Westphalia, Germany. It was built in 1929 and is one of five reservoirs on the Ruhr.
The reservoir is about 4.2 km (2.6 mi) long and has an average width of 296 meters (971 ft). It begins near the point where the Lenne flows into the Ruhr, and ends with the weir and hydroelectric plant of Hengsteysee. The Klusenberg, a hill that is part of the Ardey range, is located just north of the Hengsteysee. There is also a pumped-storage plant on this reservoir, named Koepchenwerk after Arthur Koepchen.
Hengsteysee fulfills the following four functions:
- functions as the lower reservoir of the Koepchenwerk pumped-storage plant
- performs biological purification of water from the Lenne
- deposit of sediment from the Lenne
- venue for water sports and tourism