Over the last hundred years the parameters used for studying the plankton of Lake Geneva have been diversified. ln particular the quantitative approach has been made more precise and the number of measurements and amount of data has increased considerably. The increasing attention paid to water samples highligths the seasonal and plurianual changes of the plankton communities formerly considered as stable. By means of recent examples, the variation of certain criteria shows the fluctuations of the perturbed environment in its biogeochemical state.