The Hengsen Reservoir, also known as Geisecker See, is located on the Ruhr River in the natural area between Holzwickede and Schwerte and is an important component of Dortmund's drinking water supply. It was created in 1937 by the Hengsen Waterworks of the Dortmund Energy and Water Supply (DEW). Unlike the large Ruhr reservoirs, it is filled with Ruhr water through a weir and serves primarily for sedimentation, groundwater recharge, and as a buffer basin in the waterworks system.
With an area of approximately 22 hectares, a length of approximately 1,055 meters, and a width of 182 meters, it lies in the middle of the shallow bush and forest area of the Bahnwald Nature Reserve – an approximately 80-hectare protected area established in 1992. In the center of the lake is a small island, formerly wooded, now a breeding ground for cormorants, whose activity has, however, led to a radical decline in vegetation.
The lake has relatively little tourist development: A hiking trail runs along the western shore, offering only a few views of the water – ideal for peaceful strolls or photo stops in nature. Komoot ratings show that many hikers and cyclists appreciate the combination of tranquil forest, water views, and the occasional visible waterworks infrastructure.
The northern shore borders directly on the protected Bahnwald forest, whose species-rich deciduous forests and wetlands are protected. The facility itself is largely fenced and largely separated from recreational activities by water protection regulations: Swimming, boating, or fishing are not permitted – only anglers find vague indications of isolated fish populations, such as pike, but no official regulations.
Another nearby highlight is the Hengsen hydroelectric power station, part of the waterworks with two Kaplan turbines, which began operation in 1937. The information center “aqua publik” is also located here, which takes part in the Route of Industrial Heritage and offers visitors technical insights.