Lake Geneva

Lake Geneva lies between the Alps, Jura and Geneva. Its vast crescent-shaped basin is shared by Switzerland and France. The volume slows changes in level and mean temperature, while wind can still move the surface and temporarily produce differences between opposite shores.

The Rhône brings water and sediment from Valais into the eastern lake. The Dranse, Venoge and Aubonne add to the balance; the Rhône starts again in Geneva. Because main inflow and outlet are far apart, water and heat spread through the basin and a Valais peak reaches the Seujet in muted form.

The Seujet dam regulates the lake under an international agreement. Before regulation, seasonal variation could exceed two metres; normal operation is now much tighter. An exceptionally wet or dry year is still visible: regulation organises outflow but creates no water and does not remove storage limits.

Sources may call it Lake Geneva or Léman. What matters is station, datum and time. Rhône discharge at Porte du Scex describes inflow; a level at Geneva or Lausanne describes the lake surface. The median provides seasonal context but is not a flood forecast.

The lake stores enormous heat and stratifies strongly in summer. Surface water can be warm while depth remains cold. The Bise, westerly winds and Rhône inflow alter local values. A bathing temperature belongs to a place and time; whole-lake warming requires broader monitoring.