The filtration rates of four species of eulamellibranchs (Dreissena polymorpha, Sphaerium corneum, Pisidium amnicum and Pisidium casertanum) are measured at high (14°, 15° respectively 20°C) and low (5° respectively 6°C) temperatures by an indirect method. The differences of filtration rates at high and low temperatures are significant in all classes of size. The filtration efficiency of large individuals is more dependent on temperature than that of small ones. The filtration rate "ml/g live weight and hour" of the largest animals of the species tested depend on mobility: P. amnicum, which is rather mobile compared with the other species, shows the lowest, the completely sessile Dreissena the highest values. The importance of small bivalves for the self-cleaning of waters is shown by some examples of filtration capacities per m2 of bottom approximately calculated.