About Grosse-Dhuenn Dam

The Große Dhünn-Talsperre in the Bergisches Land region of North Rhine-Westphalia is Germany's third largest drinking water reservoir by volume, holding 81 million cubic metres when at full supply level. Completed in 1985, the zoned earth-fill embankment dam stands 52 metres tall and impounds the Große Dhünn river in the hills southeast of Wuppertal. The reservoir supplies drinking water to the Wuppertal, Remscheid, Solingen, and Leverkusen area — a densely populated industrial corridor of roughly 800,000 people. Water quality protection is especially stringent: the entire catchment is designated as a water protection zone (Wasserschutzgebiet) in which synthetic fertiliser and pesticide application is strictly regulated. The reservoir works in tandem with the smaller Vorsperre Große Dhünn upstream, which functions as a settling basin and quality buffer. The Dhünn valley ecosystem is notable for its populations of fire salamander, kingfisher, and various highland meadow plant communities. Recreational activities are restricted to protect water quality, though a cycle path runs along the eastern shoreline. The reservoir is operated by the Wupperverband, which publishes real-time fill level data and water quality reports for stakeholders in the region.