The Langer See is a lake situated in the south-eastern outskirts of Berlin, the capital city of Germany.

The lake is aligned south-east to north-west and forms part of the course of the River Dahme.

The Dahme flows into the Langer See from the Zeuthener See, at the south-east end of the lake by the Berlin suburb of Schmöckwitz.

The F12 crosses from Müggelbergallee (in Köpenick) to Wassersportallee (in Grünau), and operates all year.

The F21 crosses from Krampenburg via Große Krampe (both in Müggelheim) to Zum Seeblick (in Schmöckwitz), and operates only in summer.