Abstract
The aim of the paper was to investigate the impact of the eutrophic dam reservoir on the fauna of Trichoptera of the mediumsized River Bystrzyca in the area of the Lublin Upland. Material collected at three sites above and three sites below the reservoir was analyzed with respect to: species composition and diversity, dominance and trophic structures, essential physical and chemical parameters of water, both at the species as well as assemblage level. The obtained results indicated the unfavorable influence of the reservoir on Trichoptera which was expressed by the decrease in the number of species and diversity below the dam, the disturbances of dominance and trophic structures as well as the increase in the number of specimens of the species insensitive to pollution. The more detailed characteristic of the representatives of the family Hydropsychidae is also given - their distribution and preferences against habitat conditions in the arrangement: river-reservoir-river.