Lake Geneva

Lake Geneva traces a crescent 72.8 km from east to west, less than 14 km across at its widest, between the foot of the Jura and the first Alpine ranges. Its surface of 580.1 km² makes it the largest lake in Western Europe; the water reaches 309.7 m below the surface, for a mean depth of 152.7 m. The Franco-Swiss border follows the axis of the lake: the northern shore and both tips belong to the cantons of Vaud, Geneva and Valais, the southern shore to Haute-Savoie. Of 200.2 km of shoreline, 58 are French.

The Rhône crosses the lake from east to west and supplies 75% of its inflow on its own. Since 1884 the level has no longer been left to rain and meltwater: it is regulated artificially within a narrow band, between 371.7 and 372.3 metres. Two basins of unequal size answer one another, the Grand-Lac to the east and the Petit-Lac between Yvoire and Geneva.

The shores, for their part, have changed hands and substance. In 2006 the international commission responsible for protecting the lake's waters found only 3% of the shoreline still wild; about 60% of the banks and their surroundings had been developed, riprapped, paved or taken into private hands, the remainder divided between semi-natural meadows and farmland. Geneva, Lausanne and Montreux on one side, Évian-les-Bains and Thonon-les-Bains on the other, punctuate a shore shared by 65 municipalities.

The name is older than the maps that carry it. Léman goes back to an Indo-European root that already means lake: saying lac Léman says it twice, a pleonasm fixed by usage since antiquity. Strabo writes lemanè limnè in the first century BC, Julius Caesar lacus lemanus in 58 BC. The Middle Ages preferred lac de Lausanne, the sixteenth century lac de Genève; the Swiss national map kept that last form for the whole body of water until 2003, then reserved it for the Petit-Lac alone.

Why this place is remarkable

What makes Lake Geneva striking is the gap between its bulk and what can actually be seen of it: 580.1 km² and 309.7 m of depth, yet an arc closed enough that no single shore shows the whole. It is also a lake shared by two states, its border following the axis of the water since the Treaty of Lausanne of 1564, and a regulated lake, held since 1884 between 371.7 and 372.3 metres.

History and origin

The origin of the basin long divided geologists. Three schools followed one another from the second half of the nineteenth century to the 1970s — tectonic influence, river erosion, the work of glaciers — and the tectonic hypothesis held the upper hand for a long time. Seismic imaging of the lake bed carried out in the 1980s tipped the balance towards overdeepening by the Rhône glacier during the Quaternary glaciations. The lake itself took shape as that glacier withdrew, close to 16,000 years ago. The same encyclopedic source nevertheless keeps, in its summary, an older wording that assigns the Grand-Lac to tectonic folding and the Petit-Lac to the glacier: the disagreement is reported here rather than settled.