Groß Glienicker See is a lake in the states of Brandenburg and Berlin, Germany. At an elevation of 31.6 m, its surface area is 0.66 km². The border between the city of Potsdam and the city of Berlin runs in a north-south direction through the center of the lake, with the Potsdam locality of Groß Glienicke on the left shore and the Berlin locality of Kladow on the right shore.
The border between West Berlin and East Germany in the center of the lake was marked by buoys. The Berlin Wall on the west and south shores prevented access to or even a sight of the shore by East Germans. For those in West Berlin the lake was a popular place for swimming. One could swim (or in the winter walk over the ice) up to the buoys.