Adsorption of a “conditioning”; film precedes the development of communities typically dominated by diatom slimes, filamentous algae or invertebrates. The type and extent of fouling is often specific to a particular location, being influenced by water chemistry, eutrophication and whether any local control measures are employed. The zebra mussel,Dreissena polymorpha, and its rapid spread in North America, makes it probably the most economically important fouling organism in freshwaters at the present time. The types of fouling control measures in current use and future developments are discussed.