The Mettma, a mountain stream in the Black Forest, W. Germany, was investigated for effects of input of nutrients and energy by domestic waste water and effluent from a brewery introduced at one specific point. The investigation time ranged from May 1970 to February 1971. Initially, there is an impoverishment and structural changes of the biocoenosis in the hyporheic interstitial. There is an almost complete O2-depletion immediately after the waste water has been added. In winter, temperatures in the interstitial were higher than those in the current. No direct correlation between population densities and amount of organic matter were observed where allochthonous nutrients had been added. Population densities of multicellular animals were from 0 to 1.2 X 105 per 0.1 m3 of sediment. 4.1 km further downstream the fauna is similar to that above the waste water inlet, while at 7.35 km downstream of it is slightly less dense.