At the beginning of the century not all wastewaters in the Ruhr river basin were treated in wastewater treatment plants, and wastewater treatment technology was primarily limited to mechanical processes. Therefore, to keep the Ruhr water clean enough for drinking water production, it was necessary to build impounded lakes to serve as natural river water treatment plants. Thanks to reduced flow velocity and longer flow times in the impounded lakes, setteable solids are removed from the river water. Moreover, the additional water surface increases the effect of sunlight and wind, enhancing oxygen uptake and promoting biological biodegradation processes in the water.
Even with today's enhanced wastewater treatment technology, impounded lakes are indispensable for fine screening, especially for inflowing stormwater. As a result of biological self-purification, river water quality is considerably improved when the river water passes through the impounded lakes.
All impounded lakes are used for hydro-electric power generation. For this purpose, hydro-electric power plants have been constructed at the impounded lakes. Taken together, the impounded lakes have a capacity of 28.1 MW, generating approximately 92.5 million kWh annually.
For more information, please see Hydropower stations at impounded lakes.
From the outset, numerous possibilities for leisure activities were envisaged when the Ruhr impounded lakes were created. Over the years, the impounded lakes have evolved into significant local recreation areas. In addition to the water surface itself, the banks also offer possibilities for various activities, such as biking, hiking, running, inline skating, fishing, rowing, sailing and canooing.