Lake Thun (German: Thunersee) is an Alpine lake in the Bernese Oberland in Switzerland. It takes its name from the city of Thun, on its north western shore.
The lake is fed by water from Lake Brienz to the south east, which lies 6 metres higher than Lake Thun, and various rivers in the Oberland, including the Kander. Lake Thun was created after the last ice age and was originally part of the historic combined Wendelsee (”The Spiral Lake”). Passenger ships have operated on the lake since 1835 and there are currently ten passenger ships in total, operated by the local railway company BLS Lötschbergbahn.