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Lake in Switzerland and France

Lake Geneva ( lə lemɑ̃, lac Léman lak lemɑ̃, rarely lac de Genève lak də ʒ(ə)nɛv; ; Genfersee ; ) is a deep 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. Sixty percent of the lake belongs to Switzerland (the cantons of Vaud, Geneva and Valais) and forty percent to France (the department of Haute Savoie).

While the exact origins of the name are unknown, the name Lacus Lemanus was in use during the time of Julius Caesar. Lemannus comes from Ancient Greek Liménos Límnē (Λιμένος Λίμνη) meaning "port's lake". It became Lacus Lausonius, although this name was also used for a town or district on the lake, Lacus Losanetes, and then the Lac de Lausanne in the Middle Ages. Following the rise of Geneva it became Lac de Genève (translated into English as Lake Geneva), but Le Léman was the common name on all local maps and is the customary name in the French language. In contemporary English, the name Lake Geneva has become predominant.

Due to climate change, the average temperature of deep water (more than deep) increased from in 1963 to in 2016 (an increase of in 53 years), while the average temperature of surface water ( deep) increased from in 1970 to in 2016 (up in 46 years).

Lake Geneva (and particularly the lakeside parts of the city of Geneva) can be affected by the cold Bise, a northeasterly wind. This can lead to severe icing in winter. The strength of the Bise wind can be determined by the difference in air pressure between Geneva and Güttingen in canton of Thurgau. The Bise arises when the air pressure in Güttingen is higher than in Geneva.

In 563, according to the writings of Gregory of Tours and Marius Aventicensis, a tsunami wave swept along the lake, destroying the fort of Tauredunum and other settlements, and causing numerous deaths in Geneva. Simulations indicate that this Tauredunum event was most likely caused by a massive landslide near the Rhône delta, which caused a wave high to reach Geneva within 70 minutes. In 888, the town was part of the new Kingdom of Burgundy, and, with it, was absorbed into the Holy Roman Empire in 1033. In the late 1960s, pollution made it dangerous to swim at some beaches of the lake; indeed, visibility underwater was near zero. By the 1980s, intense environmental pollution (eutrophication) had almost wiped out all the fish. Endemic whitefish species Coregonus fera was last recorded in the lake in 1920 and is now extinct. Although the name fera is still used for the only coregonid present in the lake, this is not the original species but the introduced C. palaea. Today, pollution levels have been dramatically cut back, and it is again considered safe to swim in the lake. Major leisure activities practiced include sailing, wind surfing, boating (including water skiing and wake boarding), rowing, scuba diving, and bathing. A total of four submarines have plied the depths of Lake Geneva. In 1964, Jacques Piccard launched a tourist oriented submarine, the Auguste Piccard (named for his explorer father), for the Swiss National Exhibition, meant to honor the Expo 64 theme of accomplishments by Swiss engineers and industry. After operating through to 1965 in Lake Geneva, Piccard used the vessel for scientific exploration in other parts of the world. French mathematician Jacques Charles François Sturm and Swiss physicist Daniel Collodon used two moored boats, separated by a measured distance, as the transmitting and receiving platforms for the sounds of exploding gunpowder. The loud airborne sound coupled into the lake, establishing a loud underwater sound that could be measured at a distance. The flash of the exploding gunpowder provided the visual starting cue for the timepiece, and the underwater explosion sound striking a bell provided the finish cue. The lake is rich in wildlife, especially birds: both the common buzzard and the red kite breed here in considerable numbers.

Yacht racing is a popular sport, and high performance catamarans have been developed specifically for the lake. The design of the Alinghi 5, the defender of the 2010 America's Cup, was influenced by those racing catamarans. The Tour du Lac rowing event also takes place on Lake Geneva. Competitors row once around the entire lake, making this event the longest non stop rowing regatta in the world. Several competitions for swimmers are organised yearly, including the crossing of the lake from Lausanne to Evian (13km), from Chillon Castle to Geneva (70km), from Montreux to Clarens (1.8 km), in Geneva (1.8 km), all in summer, and the [[Winter swimming#Switzerland, 125m in Geneva in December.