In water bodies, stones, aquatic plants or the substrate often feel slippery. The cause of this is the so-called biofilm, a wafer-thin layer of countless microbes. They form the basis of aquatic food webs, cleaning and detoxifying the water by breaking down organic pollutants. Using lakes in the French Pyrenees as an example, researchers from the Institut National Polytechnique de Toulouse and the IGB have now shown that the microbial biofilm composition is changing rapidly as a result of climate change and that toxic cyanobacteria are increasing.