a lake in Switzerland, among the northern foothills of the Bernese Alps, at an elevation of 558 m. The lake, which lies in a tectonic depression, has steep wooded shores. It covers an area of 47.8 sq km and has a maximum depth of 217 m. The Aare River, a tributary of the Rhine, flows through the Lake of Thun and the Lake of Brienz, which is at a higher elevation. The Lake of Thun freezes for periods of six to seven months. There is navigation on the lake; lakeside resorts include Spiez and Hilterfingen, and the city of Thun is near the lake.