Discovering high-altitude lakes: origins, bathing and impacts
While hiking in the mountains on a hot summer's day, you may come across a high-altitude lake with cool, crystal-clear water. The idea of taking a dip, or simply dipping your feet in the water, might then cross your mind. Because yes, even at an altitude of over 2,000 metres, the water isn't always as icy as you might think...
Where do these lakes come from? How were they formed? Can you swim in them, and what are the impacts of bathing in these fragile environments?
We'll explain everything. Tie your shoelaces, pack your rucksacks... and off you go!
High-altitude lakes are very fragile environments
By the way, what is a high-altitude lake?
Unlike the Mont-Cenis artificial lakeUnlike the Mont-Cenis artificial lake, high-altitude lakes are water bodies located at altitudes of over 2,000 metres, and can be quite deep. These lakes are the result of glacial activity. Glaciers carve depressions in the rocky ground - when the glaciers melt, these depressions fill with water, creating high-altitude lakes.
Their unique environment, marked by lower temperatures and specific ecosystems, makes them particularly sensitive to climate change and possible human pollution.
The importance of high-altitude lakes
Today, there are several high-altitude lakes scattered around the Haute-Maurienne Vanoise region and its six resorts: Valfréjus, la Norma, AussoisVal Cenis, Bessans and Bonneval sur Arc.
These high-altitude lakes play a crucial role in regulating water resources, acting as natural reservoirs that gradually release water from precipitation and snowmelt to the surrounding valleys and plains.
In addition to their hydrological importance, lakes are home to a rich biodiversity with plant and sometimes animal species that have adapted to the harsh conditions of high altitude.
However, these lakes are vulnerable to the impacts of global warming, such as shrinking glaciers, and increasing pressure from human activities such as tourism, agriculture and urbanization. Preserving these ecosystems is therefore essential to maintaining their ecological balance.
Is swimming permitted in high-altitude lakes?
Lac Sainte-Marguerite, Lac Noir and Lac de la Partie Lac de la Partie... There are a number of splendid spots here that might just tempt you to dip your toes in the water... or even take a dip.
- Is it possible?
- Yes, but we strongly advise against it.
So why is swimming not recommended?
Although bathing in high-altitude lakes is neither "officially" prohibited nor otherwise regulated, it is nonetheless inadvisable - both in terms of environmental quality and human health.
Protecting lakes is crucial, and we all need to pay special attention to them or risk losing a precious part of our common heritage simply for the sake of it. There are many reasons for this:
Chemical pollution
First of all, it's important to remember that high-altitude lakes are "sentinel" environments, so they react very quickly to external changes in their environment. Sun creams, used by hikers to protect themselves from UV rays, often contain chemical components, including endocrine disruptors. These substances can find their way into the water when introduced directly by bathing, splashing or by the utensils and crockery used by hikers when bivouacking.
Shoreline erosion and bottom disturbance
Swimming in a high-altitude lake can cause silt and sediment to resuspend on the lake bottom. Once in suspension, this silt clouds the water quality and reduces light penetration.
Disturbance of breeding and refuge areas
The shores of high-altitude lakes are often crucial areas for fish and frog reproduction. Trampling the banks and swimming in shallow areas can damage these habitats and increase stress for these aquatic vertebrates.
What about our health?
Thermal shock risks
During heatwaves, we remind you that it's essential to stay hydrated and in the shade as much as possible. When you go hiking in the sun, or bikeyour blood vessels dilate, making them more vulnerable to sudden changes in temperature - in this case, hot/cold.
If, after a long walk, you stop to take a dip in an icy lake, your body can quickly find itself put to the test, with disastrous consequences: a sharp drop in blood pressure, the retraction of veins and, in more serious cases, stroke...
If you feel unwell or experience any serious symptoms, remember to immediately contact emergency services by dialing 112. Because of the mountain environment, it can take a long time for the rescue team to intervene. So you need to be extra careful.
Because swimming isn't safe
A mountain lake is neither the sea nor the swimming pool of O'soi. Above all, it's an unsupervised natural environment. So it's important to be aware of the dangers that await you there - there won't be a lifeguard to come to your rescue, for example.
Water quality is not controlled, and some lakes contain bacteria.
A common heritage to preserve
Phillipe LHEUREUX, Deputy Director of the Vanoise National Park, explains: "High-altitude lakes are very fragile environments. They are particularly sensitive to the slightest physical or chemical change, and have very low resilience. That's why scientists call them sentinel environments. He adds: "Any disturbance, however trivial, will have repercussions on the biotope's equilibrium that will very quickly become irreversible. The stakes involved in protecting these high-altitude lakes - which are already directly threatened by the consequences of climate change - deserve the interest and respect of us all, at the risk of losing an entire part of our common heritage for the sole benefit of the fleeting leisure of a minority of visitors."
So where can you swim in Haute-Maurienne Vanoise?
Haute Maurienne Vanoise offers a wealth of aquatic activities; the Ludi'lacs area in Bessans is an ideal place to relax and swim with family and friends - young and old alike. In addition to swimming, there's a wide range of activities on offer, including paddle-boarding, snack bars, a pétanque area and beach volleyball. at the Val Cenis swimming pools, Aussois and Modane or at La Norma aquatic leisure center.
A little bonus: if you like water sports, you can also visit the Mont Cenis nautical basenautical base, right next to the lake, for kayaking. Nearby, you can also try your hand at canyoning - a fun experience open to all.
Vanoise National Park
