This article discusses the features of the hydrological and hydrochemical regime of the Yessil river, as a transboundary river of the Republic of Kazakhstan and the Russian Federation. In General, the hydrological regime of the Yessil river is acceptable for most freshwater fish species. The maximum permissible concentration for fishery reservoirs is exceeded annually for the entire length of the river in terms of ion content only for sulfates from 1.1 to 1.7 times. The main pollutants of the Yessil river are storm runoff from the territories of settlements, as well as mineral and organic fertilizers washed away by meltwater and rainwater from catchment areas.