Summary:

This article is concerned with surface water quality with regard to the identification of its main factors influence on water quality state on the basis of two selected low-retention reservoirs in the Podlaskie. The aim of the work was to evaluate the pollution level in the reservoirs in Korycin and in Wasilków, and also to determine the seasonal changes in the contents of the selected physio-chemical indicators in characteristic measurement and control points of the reservoirs, from April 2007 to March 2008. There are many factors which affect the quality of the water in the reservoirs, for instance the natural processes of self-purification which occur with the participation of plant and animal organisms. The progress of the process being in the reservoirs as well as water outflowing quality depends on the water contamination degree that supply the reservoirs. The highest concentration of the analysed parameters were obtained in the reservoir in Wasilków. The water in Korycin had better quality. Most of the analysed physic- chemical indicators of water in both reservoirs were equivalent to I/III quality class, but colour, phosphates and COD-Cr were the disqualifying parameters of water quality. The reservoir in Korycin indicates a self-purifying capacity, whereas it was not determined this kind of process in the one in Wasilków.