The fish community biomass (B), abundance (A) and production (P) of the Volynka Stream, Bezdrevsky Brook nad Vltava River influenced by organic waste waters were estimated. The dominant trout population was strongly affected by pollution, values of A, B, P decreased from 1,264 inds.ha-1, 85.6 kg.ha-1 and 76.2 kg.ha-1 to 92 inds.ha-1, 9.8 kg.ha-1 and 5.9 kg.ha-1 in Volynka Stream, from 10,496 inds.ha-1, 200 kg.ha-1 and 215 kg.ha-1 to 0 in Bezdrevsky Brook (for the Vltava River we do not know "unpolluted state", following values of A, B and P were found below the inflow of pollution: 66 inds.ha-1, 5.6 kg.ha-1, 4.9 kg.ha-1. The trout population regenerates after 5-6 km in Volynka Stream and the Vltava River. In the Bezdrevsky Brook the trout population was replaced by cyprinids and perch. The growth rate of trout in polluted sections was obviously higher, the proportion of younger age groups lower. The saprobity index according to Sladecek et al. (1981) gives lower values of saprobity when calculated for the fish community compared to those calculated for macrozoobentos community. Values of fish saprobity and diversity indices were found to be inadequate for the description of community changes due to organic pollution, quantitative data are necessary.