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THE 4 SEASONS OF LEMAN

To what extent does the lake warm up or cool down during the year? How does its oxygen level change? And how does its transparency and the development of algae fluctuate? To better understand how it works, follow the evolution of the lake through the seasons.

Lake Geneva in summer

In summer, the lake is divided into three superimposed water layers: the epilimnion (warm), the metalimnion (warm), the hypolimnion (cold).

The algae suspended in the water continue to grow in the epilimnion and metalimnion where they have sufficient light and nutrients (mainly nitrogen and phosphorus). The more algae there are, the less transparent the surface water becomes.

Algae are important for the functioning of the lake as they form the basis of the food chain. Most of them are not a problem, but some species are problematic: those that clog fishing nets, and toxic cyanobacteria.

The temperature of the waters of Lake Geneva in summer

In summer, the lake is divided into three layers of water. The epilimnion, located between the surface and about 10 m depth, is the layer that is almost homogeneous in temperature. Below this, the metalimnion is the layer where the temperature decreases rapidly with increasing depth. It is located at a depth of about 10 m to 30 m. Further down, the hypolimnion is the layer of cold, almost temperature-homogeneous water between the bottom of the metalimnion and the bottom of the lake. The metalimnion acts as a barrier and prevents the waters of the epilimnion and hypolimnion from mixing.

Measurement stations

Lake Geneva is monitored by two measuring stations: station SHL2, located at the deepest point of the lake (309 m), is monitored by CARRTEL of INRAE in Thonon-les-Bains and station GE3, located in the lesser lake where the depth is 70 m, is monitored by the Geneva Water Ecology Department. The previous data recorded at station SHL2 can be downloaded from the OLA website.

Newsletter

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Limnological bulletin

Discover the latest data on temperature, Secchi transparency, turbidity and chlorophyll a concentration and their evolution.

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