At 48.3 km2 (18.6 sq mi) in surface area, it is the largest Swiss lake entirely within a single canton.

[2] The culminating point of the lake's drainage basin is the Finsteraarhorn at 4,274 metres (14,022 ft) above sea level.

[3] Lake Thun's approximate 2,500 square kilometres (970 sq mi) catchment area frequently causes local flooding after heavy rainfalls.

Ten passenger ships, operated by the local railway company BLS AG like Blümlisalp, serve the towns of Interlaken and Thun; the Interlaken ship canal and Thun ship canal connect the lake to Interlaken West railway station and Thun railway station respectively.

[4][5] Following World War II and up until 1964, the Swiss Government disposed of unused munitions into Lake Thun.