Lake Geneva (French: le lac Léman or le Léman[lə (lak) lemɑ̃], sometimes le lac de Genève [lə lak də ʒ(ə)nɛːv], German: Genfersee [ˈɡɛnfərˌzeː]) is a lake on the north side of the Alps, shared between Switzerland and France. It is one of the largest lakes in Western Europe and the largest on the course of the Rhône. 59.53% (345.31 km2 [133.32 sq mi]) of it comes under the jurisdiction of Switzerland (cantons of Vaud, Geneva, and Valais), and 40.47% (234.71 km2 [90.62 sq mi]) under France (department of Haute-Savoie).

Lake Geneva has been explored by four submarines: the Auguste Piccard and the F.-A. Forel, both built by Jacques Piccard, and the two Mir submersibles.