Eixer See

It is a former gravel pond, which was developed into a local recreation area after the end of gravel mining and opened for swimming. The lake was originally created in 1949 to extract material for filling underground cavities of the Peine pit, which had been created in the course of iron ore mining. The sand extracted from wet mining with a suction excavator was transported to the colliery site by a siding. From a shaft bunker, the sand in the sink was mixed with circulating water and flushed via pipelines into the abandoned mining cavities.
The bathing lake is home to a number of leisure facilities and also has a DLRG watch station. Since 1997, the bathing water quality has been at the highest rating level.

Wikipedia