Eutrophication in Lake Geneva (= Lake Leman) appears primarily as changes in chemical characteristics and plankton populations, inducing quantitative changes in the rotifer assemblages and species combinations. In the course of eutrophication, an increase of the rotifer abundance was found, together with settlement of new species and increase of eutrophication tolerant species, and despite the decrease or disappearance of eutrophication sensitive species. The new equilibrium in the trophic state of Lake Geneva related with the decreasing inputs of nutrients, induces a new structure and less abundance of the total pelagic rotatorian community.