The paper presents the effects of the dam reservoir in Komorów on the water quality in the Utrata river. The implementation of the adopted objective involved a comparison of water quality at two points, above and below the reservoir. The Utrata River is polluted with biogenic compounds throughout the whole section studied. COD content also indicates significant contamination exceeding permissible limits. A positive effect of the reservoir on water quality in the river was also observed in terms of the content of dissolved oxygen, with concentration increasing below the reservoir. The reservoir had a positive effect on reducing the concentration of total phosphorus in the water. Water in the Utrata below the reservoir showed higher values of chemical oxygen demand (CODMn) than above the reservoir. There were no differences in the concentration of NH4+ and NO3- ions in the water before and after the reservoir.
Keywords: Biogenic compounds; Chemical oxygen demand; Dam reservoir; Water pollution.