The paper concerns to study of grain composition and contamination content in bottoms of Mściwojów reservoir. It has been constructed on stream Wierzbiak in 2000, in Dolny Śląsk province, and its main function is water supply of agriculture. Drawing of samples has been performed in 2002 and 2007. Study results showed that the bed material from primary settling tank is mainly dusty sands and fi ne sands, which constitutes about 80%. To main tank the fi ne fractions with size d < 0.25 mm delivers less than to primary part. Above mentioned fractions accumulate the most pollutions and constitute potential source of impairing of water quality. From study of cadmium, copper, nickel, lead and zinc in bottoms follows that are the I-st or II-nd class of purity.