The research concerned the Wapienica dam reservoir, which is located in the Polish Carpathians, near the city of Bielsko-Biala. The dam closes the flow of water from the 11.1 km2 catchment. The forests cover about 90% of the catchment area, while the rest of the catchment constitutes grassland areas. The reservoir has a capacity of 1.05 million m3. The collected water is intended for supplying a water supply system. The catchment is treated as semi-natural, because within its borders the only works related to forest management are carried out. The aim of the research was evaluation of the water quality in this reservoir, including trophic status, based on the analyses carried out in 2015. It was found that the water was of good quality in basic physicochemical terms (e.g. suspension ≤13 mg•dm–3, CODCr ≤11 mgO2•dm–3, conductivity ≤82 µS•cm–1, phosphates <0.05 mg•dm–3, nitrates ≤5.1 mg•dm–3, dissolved iron ≤0.12 mg•dm–3). The contamination with heavy metals was not ascertained, with the exception of the zinc. The assessed sanitary indicators are worse –the bacteria of the Coli group and periodically also enterococci were observed in the reservoir water. The reservoir is not homogeneous in terms of biological production (the trophy degree). It is low in the upper part (oligotrophy generally) and increases in the part near the dam (mesotrophy, also eutrophy). The established presence of dangerous bacteria and symptoms of the reservoir eutrophication are disturbing in the context of the opinion on the purity of uninhabited mountain areas.