The Dobczyce Reservoir is one of the new man-made lakes located at the Raba River in the Carpath-ian Mountains. The drainage basin is underlain by flysch with a high proportion of sandstone. The river is characterized by great variability of runoff. The mean annual discharge is about 12 m3·s-1. The dam began to function in 1986 and about 2.1 m3·s-1 of fresh water has been withdrawn from the reservoir to Cracow. The model was calculated for estimating Raba River discharge down the reservoir. Analysis of the river discharge before and after the dam construction has shown that one of the most important effects of the Dobczyce Reservoir is a change of the Raba River runoff: mean minimum and maximum monthly dis-charges increased and mean monthly discharge decreased.