In the context of construction of the Włodzienin Reservoir in Poland, the water quality of the main tributaries (Troja River – five sampling points, Braciszowski Brook and Levicki Brook – one sampling point each) was investigated from January to December 2006. The following physico-chemical parameters were measured: NO₃^—, NO₂^—, NH₄⁺, PO₄^3-, BOD₅, pH, conductivity, and water temperature. Statistical analysis of the data allowed the classification of the water pollution indicators according to ordinances of the Polish Ministry of the Environment. Strong pollution of the streams was revealed and consequences for water quality of the Włodzienin Reservoir were assessed. The reservoir will be stabilized and thermally stratified in summer. Because of the polytrophic conditions, it will be strongly affected by mass developments of phytoplankton in the epilimnion and anaerobic conditions in the hypolimnion. Some measures that can be taken to improve the trophic situation of the reservoir are discussed.