For your health
Watch out for thermal shocks! The water from mountain lakes is generally very cold. Enough to surprise your organization already overheating after a few hours of walking. In addition, some underwater currents are difficult to detect outside the lakes, however they can exist.
The water of the lakes is not treated, the quality not being monitored … It is impossible to know if it is contaminated by certain microbes or cyanobacteria, which can be responsible for skin, digestive or nervous disorders. The bacteriological risk is therefore present.
A fragile ecosystem
Human activity disrupts ecosystems. Waste left after a bivouac, pollution, involuntary introduction of bacteria … The sunscreen you apply to the body is diluted in the waters, disturbing ecosystems. This poses a major problem, the waters of the lakes are not very renewed.
The ecosystems of these lakes are fragile. They contain animal and plant species often invisible to the naked and sensitive eye. A simple swim can damage these natural environments. There is a risk of introduction, although incorporating your part, of unknown viruses of these ecosystems, which participate in its destruction.
Not prohibited, but …
Finally, if it is not strictly forbidden to bathe in mountain lakes, certain areas are still prohibited for swimming according to the prefectural decrees in force. Remember to consult them before leaving.