The aim of this study was to analyze the efficiency of wastewater treatment processes in fifteen wastewater treatment plants located in the region of Lake Czorsztyn, which functions as both a direct and indirect receiver of treated effluents from these facilities. The analyzed wastewater treatment plants are situated in the following localities: Czarny Dunajec, Czorsztyn, Dębno, Frydman, Kluszkowce, Krempachy, Krościenko, Łopuszna, Maniowy, Niedzica, Sromowce Niżne, Sromowce Wyżne, Szczawnica, Trute, and Trybsz. The assessment of treatment efficiency in these facilities was performed based on the calculation of the average reduction degree (η) of selected pollution indicators (BOD₅, CODcᵣ, total suspended solids, total nitrogen, and total phosphorus), as well as on the analysis of the number of exceedances of their permissible values in treated wastewater. The evaluation was based on analytical results from two years (2023–2024). High wastewater treatment efficiency was found for BOD₅, CODcᵣ, and total suspended solids (the reduction range for the analyzed contaminants was: ηBOD5= 91.2%–99.1%, ηCODcᵣ = 80.9%–96.7%, ηᴛss = 88.5%–98.3%). For total nitrogen, the average reduction efficiency ranged from 48.2% to 96.6%, and for total phosphorus from 55.6% to 95.7%. Exceedances of permissible total nitrogen concentrations were observed in 40% of the analyzed samples from the Niedzica wastewater treatment plant, as well as single exceedances of total phosphorus limit valuess in Czarny Dunajec, Czorsztyn, and Niedzica.
