The effect of five small municipal sewage treatment plants (throughput from 100 m³·day^-1 to 2,300 m ·day^-1), situated on the Warta River between Oborniki and Skwierzyna, on nitrogen and phosphorus loads carried by the river was analyzed during investigations covering the period 1992/1993-2001/2002. The total share of nitrogen and phosphorus loads from sewage treatment plants in the loads in the river, calculated at the last measurement point in Skwierzyna, did not exceed one per cent. A considerably greater effect was found from non-point pollution sources and meteorological conditions, especially precipitation levels in the winter half-year.
This study analyzed nitrogen and phosphorus loads discharged to the Warta River along with treated effluents. The local effects of the concentrations of the treated effluents were not discussed.