Acta Scientiarum Polonorum

Abstract: The paper presents discharge variability of the Samica Stęszewska River in Stęszew cross-section. The study was carried out in the catchment area of 109 km² in the hydrological years 2001-2007. The results have shown that outflow distribution was dependent on the weir exploitation, which is located on the Samica Stęszewska outflow from Niepruszewskie Lake. Our study indicated that in the years of the similar precipitation the complementary index of hydrological disturbances in the Stęszew cross-section was ten times lower in 2001 (during damming) than in 2007 (without damming). Also, indexes of the monthly discharges were much lower in 2001 than in 2007. They ranged from 0.59 to 1.55 and from 0.27 to 3.72, respectively. In 2001 the exploitation of the weir increased ac-tive retention in the Niepruszewskie Lake almost two times.