Abstract. Small rivers form the water resources of medium and large rivers, hydrochemical water quality and creating lands large areas.

Purpose is determination of interdependencies between hydrochemical indicators of surface water quality on the example of a small river as a limiting factor of formation of aquatic ecosystem of territories.

Correlationi analysis of the studied indicators of wateri quality were conducted on an average valueiof each indicator (pH, phosphates, nitrates, BOD₅, COD, soluble oxygen) for the period fromi 2007 to 2021. Found a significant increase in phosphates with time. Positive changes are founded in wateri object that is related to a decreasei in the value of BOD₅. This isi due to a decrease in the numberi of use of oxygen on oxidation ofi inorganic and organic substances. In general, the use of river runoff of the riveri above normal, and the overall environmental statei of river basin is defined as “extremelyi poor”.

Periods were determined with exceedingi the MPC for hydrochemical indicators of wateri quality; the sources of the input ofi pollutants into the water object were identifiedi and analyzed. Weak correlations between BOD₅, CODi and nitrates, phosphates were determined. These confirmi the fact of increasing BOD₅ and CODi due to non-oxine-containing forms ofi phosphorus and nitrogen compounds. A further perspective is toi study ways to reduce the supply ofi phosphates to the water body.