Lake Hengstey is located near Hagen, downstream of the River Lenne’s mouth into the River Ruhr. When it was first put into operation, the chalybeate and acid Lenne waters mixed here with the alkaline waters of the River Ruhr, leading to increased sludge precipitation and creating a strong purification effect. Today, water quality of the Lenne water has been considerably improved thanks to the construction of wastewater treatment plants, and Lake Hengstey serves as a bed-load trap and fine screening step.
MMoreover, Lake Hengstey serves as a low-level reservoir for the pumped-storage hydrostation in Kerdecke (Koepchenwerk), built by the RWE energy corporation. Due to the pumped-storage mechanism, the water level of Lake Hengstey fluctuates by up to 70 centimetres. In 1988/89, approx. 400,000 cubic metres of sediment were dredged from Lake Hengstey.