The function of biofilms in natural waters is driven primarily by mutual interactions between algae, bacteria and their grazers. In turn, the grazers together with a hydraulic regime of the environment may control the biomass and the thickness of the biofilms and affect their ability to intake and retain nutrients and toxic pollutants. Thus biofilms represent the hot spots of metabolic activity which contribute substantially to water self-purification and serve as food for invertebrate organisms. However, biofilms may also show adverse effects on the surfaces they colonize. and Martin Rulík.