Foto de stock - 28 October 2021, Brandenburg, Buckow: Fred Schüler, chairman of the anglers' association ""Märkische Schweiz"", stands with a fishing rod at Schermützelsee. The Schermützelsee in Märkische Schweiz worries residents, users and conservationists. Because in one of the few clear water lakes of Brandenburg the oxygen becomes scarce - a danger for flora and fauna in the water. Inexplicable amounts of phosphate and the beaver are said to be to blame. The people of Buckow are proud of ""their"" Schermützelsee, which lies in a valley basin. The 137-hectare and approximately 40-metre-deep clear-water lake forms the centre of the ""Märkische Schweiz"" nature park, lies entirely within the town's boundaries and is known beyond the region for its bathing quality. Photo: Patrick Pleul/dpa-Zentralbild/ZB. - Buckow/Brandenburg/Germany