 It is located partly in the municipality of Erkner (Oder-Spree district) and part in Rahnsdorf, a Berliner locality in Treptow-Köpenick district.The lake forms part of the course of the River Spree, and is the location of that river's confluence with the short Flakenfließ that flows out of the Flakensee.The reach of the Spree downstream to the Müggelsee is also known as the Müggelspree.