Lake Geneva warming sparks concern

People swimming in Lake Geneva on a sunny day KEYSTONE/© KEYSTONE / CYRIL ZINGARO

The waters of Lake Geneva are warming to such an extent that biodiversity, drinking water and bathing are being put at risk. 

This alarming finding emerges from a report published on Monday by the International Commission for the Protection of the Waters of Lake Geneva (CIPEL). 

Since 2012, the temperature at the bottom of Lake Geneva has risen by one degree Celcius. This is significant, noted Nicole Gallina, Secretary General of CIPEL. At the surface, the average water temperature reached 13.6 degrees in 2022, an increase of 1.2 degrees in 30 years. 

Ther year 2022 was marked by a record heat, which also featured low amounts of precipitation and high levels of solar radiation. These conditions led to the fact that the temperature of the surface layer of the lake, between zero and ten metres, constantly exceeded monthly norms. 

The rarity of severe winters with windy episodes prevented complete mixing of Lake Geneva’s waters. This hindered the oxygen supply to the deeper layers of the lake. Today, there is no longer enough oxygen at depth to support the presence of living organisms, Gallina noted. 

Due to the lack of mixing, the nutrients essential for the development of phytoplankton accumulate at depth. However, phytoplankton is the basis of the food chain, explains the Secretary General of CIPEL. The biodiversity of the lake is therefore at risk. 

Water quality will also suffer from global warming, according to the scientific report. Lake Geneva is a source of drinking water for a catchment area of one million inhabitants. If the water is no longer drinkable, it must be treated and becomes more expensive to use. 

According to the Intergovernmental Panel on Climate Change (IPCC), Alpine lakes are more vulnerable to climate change than other bodies of water. They are warming four to five times faster than the oceans. At current rates, the temperature of their water could rise by 3.8 degrees by the end of the century. 

Lake Geneva is an oasis of refreshment, explained Gallina. The emergence of invasive species and the deterioration of water quality could cause it to lose this function. Swimming could become problematic and commercial fishing could also suffer greatly. 

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