Rantzauer Lake

The Rantzauer See is located in the city of Barmstedt in the district of Pinneberg in southwestern Schleswig-Holstein. It is about 420 by 280 meters in size, has an area of 7.5 hectares, and is no deeper than three meters.
From 1934 to 1938, the lake was excavated by hand on the orders of the Nazis by the imperial labor service. The water level of the Rantzauer See is managed by damming the Krückau, which feeds it. This intervention in nature and the associated interruption of the migration path for the local fish population caused problems in the past. Therefore, in 1981 a nine-step fish ladder was built at the dam of the castle island, allowing the fish to continue their migration to the upper spawning grounds.

Wikipedia