Lake Geneva's fish threatened by warming waters: experts
CIPEL is a joint French-Swiss organisation that monitors the picturesque, crescent-shaped body of water shared between both countries.
France's National Research Institute for Agriculture, Food and the Environment analyses water samples collected by CIPEL.
"If there is less and less oxygen in the water, there is less and less viable space for living organisms," explained Viet Tran-Khac, laboratory manager at the research institute's facility in the Thonon-les-Bains, on the lake's southern shore.
Typically in winter, the surface temperatures cool to a density comparable with the lake's deeper layers, facilitating a mixing of waters between the levels.
This natural cycle is essential for maintaining aquatic ecosystems as it transfers oxygen to the lake's lower levels.
However, this full-scale winter mixing is becoming rare, as ever-milder winters, which scientists attribute to global warming, prevent the surface waters from cooling sufficiently.
"With climate change, we no longer have the extremely cold winters needed for this natural mixing to take place,' Gallina told AFP.
In the current winter, the minimum average temperature measured in the top 10 metres (30 feet) of the lake was 7.8 degrees Celsius (46 degrees Fahreinheit): an increase of 1.5C compared to the 1991-2020 reference period.
New record
Data published Wednesday by CIPEL showed that, this year, the waters only mixed down to a depth of 110 metres -- but the lake's deepest point is 309 metres down.
Thirteen consecutive winters without complete mixing marks a "historic record", warned Gallina, surpassing the previous longest spell set between 1987 and 1999.
"During the last complete mixing in 2012, the oxygen level in the deep waters was seven milligrammes per litre," the biologist said.
It has now dropped to 2.4 mg per litre -- below the critical threshold of four mg necessary for living organisms.
However, Gallina stressed there remained "hope" for the re-oxygenation of deep waters.
Last year, a study by the Swiss Federal Institute of Technology university in Lausanne showed that the complete vertical mixing in 2012 also benefited from lateral mixing flows -- a phenomenon which was previously unknown.
However, an entire ecosystem is starting to change, warned CIPEL.
The lack of oxygen also impacts the growth of phytoplankton plants, which are eaten by zooplankton organisms -- which themselves serve as the food base for fish.
The future of Arctic char, fera and other emblematic Lake Geneva fish is under threat.
"Salmonids like fera need cold water to spawn. Before, it spawned at a depth of three to six metres; now it spawns at 20 to 25 metres," said Alexandre Fayet, president of the Swiss inter- cantonal association of professional Lake Geneva fishermen.
"For the moment, we are not too worried" but "we are trying to diversify and commercialise fish that like warmer and less oxygenated waters, such as carp, tench and bream," he told AFP.
'Transformation' phase
LeXPLORE, a floating scientific platform, has been carrying out research on Lake Geneva since 2019, studying 44 different parameters down to a depth of 110 metres.
Natacha Tofield-Pasche, its project manager, said that besides the rising lake temperatures, global warming also leads to "extreme events" that wash a lot of polluting particles down into Lake Geneva, as witnessed during major floods last year in Switzerland's Wallis region.
Such events can also knock out wastewater treatment plants, while the lake provides drinking water to around a million people.
CIPEL is "very worried because it sees that Lake Geneva is going through a transformation
phase," marked by long periods without complete mixing, said Gallina.
Added to this are other challenges, such as pollution invisible ot the naked eye, such as micropollutants and microplastics, or the invasion of quagga mussels.
In addition, high heat episodes increase the risk of proliferation of cyanobacteria, which can be toxic.
The lack of mixing also promotes the accumulation of nutrients such as phosphorus in deep waters.
In the event of increasingly exceptional complete mixing, the phosphorus could rise to the surface, causing algae blooms.
Hashtags
Try Our AI Features
Explore what Daily8 AI can do for you:
Comments
No comments yet...
Related Articles
LeMonde
13-08-2025
- LeMonde
Heatwaves deliver lasting blows to the economy
In the northern French town of Gravelines, four nuclear reactors have been shut down since Monday, August 11. In a scenario seemingly drawn straight out of a science fiction movie, a massive number of jellyfish had clogged the filters at the pumping stations that draw in seawater to cool the plant. Two days earlier, reactor number two at the Bugey power plant, in Alpine eastern France, was shut down to avoid discharging overheated water into the Rhône river, thereby protecting the local fauna and flora. These two examples highlight the consequences of climate disruption for certain economic sectors, while others stand to benefit (cinemas, shopping centers, ice cream vendors, air conditioner and portable fan sales, etc.). Since Friday, August 8, France, like the rest of Europe, has been suffocating under a heatwave, forcing many industries to adapt to scorching temperatures and compelling companies to step up efforts to protect their employees' health. On Wednesday, three quarters of mainland France were placed on alert, including five departments on red alert and 68 on orange (out of 96). On Tuesday, a temperature of 42.9°C was recorded in Saint-Laurent-du-Pape, and 42.6°C in Romans-sur-Isère, both in southeastern France. The prefect of the Rhône department, where both towns are located, suspended all outdoor construction work. To the south of the western Maine-et-Loire department, the Cholet inter-municipal authority rescheduled household waste collection to evening hours – between 7 pm and 3 am – and is only opening waste collection centers in the morning, when it is still relatively cool.
Euronews
13-08-2025
- Euronews
Europe says it leads the world in Earth Observation. But what is it?
The heavy-lift launcher, developed over a decade by the European Space Agency (ESA) and ArianeGroup, was launched from Europe's Spaceport in Kourou, French Guiana this Tuesday. After just over an hour, the satellite separated from the rocket and began its journey around the Earth. With this new satellite the EU strengthens its position as a leader in Earth observation, according to Andrius Kubilius, EU Commissioner for Defence and Space. What is Earth observation and why this matters? Earth observation is the process of gathering information about our planet's physical, chemical and biological systems – Europe relies on the Sentinel satellites from the Copernicus programme managed by the European Space Agency. From measuring Arctic ice melt to mapping deforestation, the technology allows scientists to see changes in the environment with great precision. The new satellite, Sentinel-5A, will be operated by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) and is designed to deliver high-quality data for forecasting extreme weather, tracking greenhouse gas emissions and monitoring ocean temperatures. 'Extreme weather has cost Europe hundreds of billions of euros and tens of thousands of lives over the past 40 years,' said EUMETSAT Director-General Phil Evans to Euronews. This launch is a 'major step forward in giving national weather services sharper tools to save lives, protect property, and build resilience against the climate crisis.' Timo Pesonen, Commission Director General for Defence Industry and Space said on social media his hope that the new Sentinel satellite will participate to track air quality and emissions worldwide to support EU policies like the Methane Strategy and Air quality Directive. Europe's independent path to space The satellites programme Copernicus is the world's most advanced fleet of Earth observation – however the EU lacked its own capacity to send those satellites into space. By coupling world-class satellite technology with independent launch capacity, Europe is positioning itself as a leader in both the science and infrastructure of Earth observation. Until now, Europe's space ambitions faced this practical challenge to get satellites into orbit without depending on outside players. With Russia's Soyuz rockets no longer an option, the continent had become increasingly reliant on SpaceX, Elon Musk's US-based company, for launches – an embarrassing ally.
Euronews
13-08-2025
- Euronews
Hunting microplastics: French scientists sound the alarm on plastic pollution
The Mediterranean is the sixth largest accumulation zone for marine litter. It holds only 1% of the world's waters but concentrates 7% of all global microplastics. This is why French scientists from the Exploration Bleue project have come off the coast of Toulon to study the impact of microplastic pollution in the Mediterranean Sea. Their expeditions are led by the NGO Expédition 7ᵉ Continent's 27-metre sailing vessel. 'The Mediterranean is an enclosed sea with a dense population. All human activity ends up in the sea. We study the chemical pollutants carried by plastics. What we already know is that all of them contain chemical pollution,' explains Alexandra Ter-Halle, Director of Research at the French National Centre for Scientific Research (CNRS) and scientific coordinator of the expedition. The research involves towing two trawls for one hour to collect microplastic samples. These will then be sorted in the laboratories participating in the project. Alexandra has been studying the chemical nature of pollutants associated with plastics for years at the University of Toulouse. 'We measure and weigh microplastics; we analyse their composition. We know that over 16,000 chemical substances are used to make plastics — 4,000 of them are already classified as hazardous.' When marine animals are exposed to microplastics, chemical substances can transfer into their bodies. Since many of these are endocrine disruptors, they impact the animals' health. The effects on humans are not yet fully understood, as Alexandra explains: 'We know that endocrine disruptors affect the entire hormonal system in our bodies. They impact fertility and the development of cancer, but we still have many questions about this plastic pollution.' Science is only just beginning to understand how dangerous microplastics can be for ecosystems and human health. We eat, breathe and drink them — but there's still much we don't know. For micro- and nanoplastics, which are often smaller than a thousandth of a millimetre, we lack precise tools to measure them or fully grasp their effects, scientists say. The European Commission's Zero Pollution Action Plan aims to cut microplastics by 30% by 2030. Jean-François Ghiglione, a marine microbiologist and research director at CNRS, led an unprecedented sampling campaign across nine major European rivers in 2019. He found microplastics everywhere in 'alarming' concentrations. 'Europe is quite advanced in this area,' explains Ghiglione. 'We used to have massive plastic pollution, mainly from packaging and single-use plastics. That was the European Union's initial target. Now, we're hoping to see a shift in how plastic is perceived.' So far, plastic has been viewed as waste, and efforts have focused on waste management. Ghiglione hopes the EU will drive a push for a drastic reduction in plastic production, and also come out with a list of chemical substances to be banned from use in plastics. Europe has made progress in limiting microplastics, but Ghiglione and the scientific community are calling for more. With negotiations for a global treaty still underway, Europe and the international community face a choice: continue managing pollution, or tackle the problem at its root.
