The flood situation which caused the threats of submergence of the terrains which are below the reservoir did not happen in during above forty five years of the operations of reservoirs. It was except intensive flood in the day 18 July 2010, in result which happened the submergence of settlement in Zesławice, located between Mistrzejowice and Grębałów. According to victims the cause of submergence was the uncontrolled waters outflow from the reservoirs. The preliminary analysis of the freshet inflow to reservoirs with the analysis of their outflow was introduced in this work. According to the result this analysis the impact of the Zesławice water reservoirs on the reduction of the flood wave was defined. The analysis of the flood course was worked out on the basis of the registered states of water on the watergauge of Zesławice water reservoirs, installed from the upper side of the weirs of the dam (W1) and on the water-gauge IMGW, located 300 m below the dam of water reservoirs (W2), and on measurement coss-section (W3), located 140 m below the dam of reservoirs . It was stated, that already during the first day of freshet, possibility of retention of the flood flow in reservoirs becomes limited, because of quick their fulfilment and such situation forces the outflowing the whole of the inflow to reservoirs. It was also affirmed that flood situation of 18 July 2010 had not been caused accidental, or the also uncontrolled outflow from water reservoirs in Zesławice. On the basis of the analysis of average flows twenty – four hours one can affirm that the reservoir reduced the flood wave about 4% only.

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