“…Unpolluted streams generally have low productivity (Duffer & Dorris, 1966). Primary production in river can be explained as a function of solar radiation, temperature, chlorophyll concentration and euphotic depth (Kowalczewski & Lack, 1971;Takahashi et al, 1973;Naiman, 1976 andRickert et al, 1977). Maximum concentration of chlorophyll have been observed in autumn in the Danube (Ertl et al, 1972), in spring in Kiel Bight (Bodungen et al, 1975) and Bere Stream (Marker, 1976a); in summer in the streams Dockens Water and Ober Water (Marker, 1976a).…”