This article includes an assessment of the impact of sewage exiting from the sewage treatment plant in Szczawnica before and after the modernization of the facility, the physicochemical composition and the quality of the water of their receiver - Dunajec River. The work was carried out on the basis of analysis of samples taken from raw and purified sewage and receiver waters. The Dunajec water intake was above and below the point of sewer discharge from the WWTP. The range of contaminated indicators included 14 physicochemical parameters and two bacteriological indicators. On the basis of the research conducted, it was stated that the Szczawnica Forest Enterprise after its modernization in 2016 functioned correctly. The purified sewage on it complies with the requirements of a water permit, which translates directly into effective protection against the pollution of receiver waters. This was confirmed by the results of the Kruskal-Wallis test that showed statistically significant differences between the median values of overall nitrogen concentrations before and after the refurbishment of the facility. For the remaining pollutant indices (total suspensions, BOD5, CODCr, total phosphorus), no statistically significant differences were found between the medians. In addition, it was found that the physico-chemical composition of Dunajec waters was similar in both examined sections. The purified effluent discharged from the Szczawnica treatment plant to the Dunajec River did not contribute to deterioration of its water quality in the case of physico-chemical indicators. Based on the classification of these elements, it was determined that in the analyzed period, the Dunajec water in the section directly above and below the WWTP meets the requirements for category A1 of waters intended for the supply of the population (very good quality water). In the case of microbiological classification based on the number of bacteria of the coli group and Escherichia coli, Dunajec was classified as IV and V class (unsatisfactory and poor quality water), thus excluding its water for consumption and as a potential bathing place.