Fühlinger See

Fühlinger See is a series of connected lakes in the Cologne suburb of Fühlingen in the German state of North Rhine-Westphalia.

There are equestrian routes around the lake, and the horse riding club Reiterverein Oranjehof is located nearby.

[1] The lake was created from 1912 when aggregate was excavated; according to the German Wikipedia entry, this was for what are now Bundesautobahn 4 (Aachen–Cologne) and Bundesautobahn 3 (Krefeld–Cologne), but according to a newspaper article from 1935, the fill was used for work on the railway line from Aachen to Cologne (which was indeed widened to four tracks from 1912 onwards).

5 (with entry fee), because the city of cologne fears law suits in case of accidents.

Since there are structures built in the lakes the administration fears people might think swimming would be under supervision.