The Westfälische Sand- und Tonwerke Müller & Co., today Euroquarz GmbH, operated since the beginning of the 20th century, a sand pit in the area west of the confluence of the streams Hambach and Wienbach. The sand was obtained in the wet mining by floating bucket excavator, since the pit was filled with groundwater.
After the dismantling had been stopped, the blue lake with white sand beach and clear "blue" water lured now also bathers despite official bath prohibition. After the Second World War, in the summer crowds came from neighboring cities to swim in the Blue Lake. The community owned but chargeable beach in the immediate vicinity was closed since the 1920s because of lack of visitors.
In 1955, the RWW acquired the former sand pit. From now on, the sand pit filled with groundwater was supposed to serve as a reservoir for service water and thus relieve the drinking water works in Dorsten-Holsterhausen. The largest customers are industrial companies and power stations in the area. The Scholven power plant, for example, gets its cooling water mainly from the Blue Lake. Until its closure was the colliery Prince Leopold, who used the water for steam engines, coal dust underground and used as cooling water another large customer. The RWW planted the shores of the lake and made a circular route around the lake. In 1976, the so-called seawater plant was expanded.
Source: Wikipedia