The Hengsteysee is a reservoir on the Ruhr river between the cities of Hagen

Hagen

Hagen is the 39th-largest city in Germany, located in the federal state of North Rhine-Westphalia. It is located on the eastern edge of the Ruhr area, 15 km south of Dortmund, where the rivers Lenne, Volme and Ennepe meet the river Ruhr...

, Dortmund

Dortmund

Dortmund is a city in Germany. It is located in the Bundesland of North Rhine-Westphalia, in the Ruhr area. Its population of 585,045 makes it the 7th largest city in Germany and the 34th largest in the European Union....

 and Herdecke

Herdecke

Herdecke is a town in the district of Ennepe-Ruhr-Kreis, North Rhine-Westphalia in Germany. Its located south of Dortmund in the Ruhr Area and is known as Die Stadt zwischen den Ruhrseen ....

, North Rhine-Westphalia

North Rhine-Westphalia

North Rhine-Westphalia is the most populous state of Germany, with four of the country's ten largest cities. The state was formed in 1946 as a merger of the northern Rhineland and Westphalia, both formerly part of Prussia. Its capital is Düsseldorf. The state is currently run by a coalition of the...

, Germany

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

. 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 metres (971.1 ft). It begins near the point where the Lenne

Lenne

The Lenne is a river in the Sauerland area in North Rhine-Westphalia, western Germany, a left tributary of the Ruhr.Having its source on top of the Kahler Asten near Winterberg in an intermittent spring at an elevation of 2,687 feet, the Lenne ends after a course of 128 km flowing into the...

 flows into the Ruhr, and ends with the weir

Weir

A weir is a small overflow dam used to alter the flow characteristics of a river or stream. In most cases weirs take the form of a barrier across the river that causes water to pool behind the structure , but allows water to flow over the top...

 and hydroelectric plant of Hengsteysee. The Klusenberg

Klusenberg

The Klusenberg is, at , the highest elevation on the territory of the city of Dortmund.The Klusenberg part of the Ardey Hills lies west of the Hohensyburg. To the south its slopes fall away into the Hengsteysee lake. The Klusenberg is wooded with just a few residential houses....

, a hill that is part of the Ardey

Ardey Hills

The Ardey Hills are a range of wooded hills, up to , in the territory of the cities of Dortmund and Hagen and the districts of Ennepe-Ruhr-Kreis and Unna in the German state of North Rhine-Westphalia...

 range, is located just north of the Hengsteysee. There is also a pumped-storage plant

Pumped-storage hydroelectricity

Pumped-storage hydroelectricity is a type of hydroelectric power generation used by some power plants for load balancing. The method stores energy in the form of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power is used to run the pumps...

 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