About Agger Dam

The Aggertalsperre in the Bergisches Land of North Rhine-Westphalia holds 20.1 million cubic metres and occupies a picturesque valley in the Agger river upstream of Gummersbach. Completed in 1927, the 57-metre concrete gravity dam was one of the pioneering large reservoir projects in the Wupper and Agger catchment area, built to supply water to the growing industrial towns of Gummersbach, Wipperfürth, and the broader Oberbergisches Land. Today the Aggersee, as the reservoir is locally known, is managed by the Wupperverband and supplies drinking water to approximately 150,000 people in the Oberbergisches Land district. The reservoir also provides recreational amenities including sailing and pedal boating, and the Aggertal cycle route runs along its eastern shore connecting Gummersbach to Wipperfürth. A smaller pre-reservoir, the Vorsperre Agger, sits immediately upstream and functions as a settling and quality buffer before water enters the main reservoir. Water temperature and quality data are published by the Wupperverband's online portal, which shows the Agger system consistently meeting EU drinking water source quality guidelines. During the dry summers of 2018–2022 the reservoir experienced marked drawdown, exposing the concrete wave-protection apron along the upstream face of the dam and reducing the bathing beach access area.