Lake Geneva reached a record temperature of 27 degrees Celsius this July, intensifying concerns about the long-term health of the aquatic ecosystem. According to the International Commission for the Protection of Lake Geneva (CIPEL), rising water temperatures are disrupting the food chain and hindering the natural mixing processes essential for the lake’s survival.
Ecosystem disruption and the zooplankton decline
The warming of Lake Geneva is not a recent development, but its effects are becoming increasingly visible. Nicole Gallina, secretary general of CIPEL, stated that there is significantly less zooplankton in the lake. Because zooplankton serves as a primary food source for fish, its decline threatens the stability of the entire aquatic food chain.
This warming trend is confirmed by scientific data. In January 2025, CIPEL reported that surface temperatures in 2023 reached an annual average of 13.6 °C, which is 1.3 °C higher than the average recorded over the previous 30 years.
Did You Know?
The warming trend is not limited to the surface. Over the last 25 years, the deep waters of Lake Geneva have warmed by 0.6 degrees Celsius, a trend also observed in the lakes of Bienne, Morat, and Neuchâtel.
Impact on natural water circulation
The health of the lake relies on a seasonal phenomenon known as “brassage,” or mixing. During the winter, the lake must reach a sufficiently low temperature to allow wind-driven currents to circulate oxygen and essential nutrients from the surface to the depths.
Climate change has resulted in milder winters, which hampers this process. When the water does not mix properly, nutrients become poorly distributed, further stunting the growth of plankton. This lack of circulation affects the entire vertical column of the lake, not just the surface layers.
Future of the féra and professional fishing
The warming waters are already impacting local fish populations, specifically the corégones, commonly known as “féras.” These fish are currently in decline, raising concerns about the future of the professional fishing industry in the region.
Pêcheuse (fisher) Laura Fayet suggests that salmonids could potentially adapt, noting that corégones exist in warmer Italian lakes. However, she emphasized that because climate change is occurring at a rapid pace, the fish may not have enough time to adjust to the new conditions.
How do you think the local fishing industry should adapt to the shifting biodiversity of our lakes?
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