Why the Pyrenees’ mountain lakes are turning green

I first set foot in the Pyrenees in 2006. Two years later, I began a large-scale survey of mountain lakes and amphibian populations: from east to west, I covered more than 100 mountain lakes located in the eastern Pyrenees to the Béarn region (Pyrénées-Atlantiques).

For our various projects, we came back to sample the same lakes at least once a year. Over time,…