The quality of the Soła river flowing into the dam reservoir Tresna was presented in this paper. This is the highest reservoir of so called Sola cascade, which is important in case of flood control and as a reservoir of water used for municipal purposes. The aim of the study was to evaluate the effectiveness of protective measures for water resources realized in reservoirs catchment. Presented results showed positive influence on water quality of Soła river, but some parameters has remained at unsatisfactory levels. Especially the excessive load of nitrogen and phosphorus which flows into the reservoir was observed. The last mentioned, in flood conditions, also applies to solids (suspensions). Furthermore microbial contamination was noticed as well. All those factors indicates not entirely appropriate spatial planning of basin area.