Lake Thun (German: Thunersee) is a lake in the Bernese Oberland in Switzerland. It is located just north of the Alps, at approximately 46°41′N 7°43′E. The lake is 17.5 km long and 3.5 km wide at its widest point. The surface area is 48.3 km². The maximum depth is 217 m, which gives it a total freshwater volume of about 6.5 km³. The city of Thun is located on the north side of the lake and gives the lake its name.