The FEZ Bathing Lake is a wonderful place to splash and swim in during the summer. Lined by trees and having a sandy beach, sunbathing lawn and playground, it has nothing to be ashamed of in comparison to other Berlin lakes.
The Bathing Lake is a semi-natural body of water that has been linked to rainwater management in the FEZ Berlin for several years. Rainwater draining from the main building is temporarily stored and, after passing through a soil filter (lawn filter bed) and a reed filter bed, is fed into the Bathing Lake. Germs, bacteria and suspended matter are filtered and broken down in the plant filter beds. After flowing through the beds, the water is returned to the Bathing Lake and the water cycle is closed. This combination of processes enables rainwater and lake water to be cleaned without the use of chemicals. The addition of chlorine is unnecessary.
The water quality is regularly examined by specialist laboratories, which certify that the FEZ Bathing Lake has a very good water quality. However, as there were reports of skin irritation in 2019, it was closed as a precautionary measure during the 2019 summer season. Currently, the FEZ is working closely with the Treptow-Köpenick Health Board (Gesundheitsamt Treptow-Köpenick) and the Institute for Applied Aquatic Ecology (Institut für angewandte Gewässerökologie) to find a long-term solution.
The 240 m long and 50 m wide swimming lake was opened at the same time as the open-air stage and the sports facilities in 1951 on the occasion of the III. World Festival. Before 1951, there was a wild boar enclosure in the vicinity of the Bathing Lake. In order to create the lake, trees first had to be cleared. Then the sandy soil was dug up to a depth of about two meters and the bottom was sealed with loam and clay so that the water could not seep away.
Not far from the lake there used to be a small, inconspicuous stream. The pumping station of the waterworks and the embankment of a railway line had caused it to dry up. The result was mud and later a black, impermeable, rich soil. In order to prevent the water accumulating on the black layer of earth from escaping into the lake and indenting the clay layer, rubble was added instead of the black, rich soil. This allowed the water to seep away. To disinfect the water, it was necessary to treat it with hypochlorous acid and copper sulphate. In 1955 a chlorine, caretaker and equipment house for the Bathing Lake was built. The 4 m long water slide was built in 1958 based on the model of the water slide of the seaside resort Wendenschloss, with small specific changes.
The lake was supplied with groundwater and chlorinated until 2014.