In the article, the water composition data for Izh reservoir, the Izh river and 4 of its tributaries are provided. It includes 13 criteria: pH, hardness, total dissolved solids, concentration of nitrates, nitrites, ammonium, orthophosphates, sulphates, silicon, iron, chlorides, calcium, and hydrocarbonates. Also, the list of algal species found in the samples, which includes 84 species and intraspecies taxa, is published. The space dynamic of chemicals (along with ratio of mineral forms of nitrogen and phosphorus DIN/DIP and nitrogen and silica DIN/Si) and the influence on algal flora are discussed. Decrease of algal diversity from tributaries to the reservoir and to the section of Izh river flowing through urban area and accompanying change of environmental conditions from P-limited to N-limited were found to be bound up with significant influence of surface water run-off from the city’s territory on water composition of the Izh river and Izh reservoir.