Kharanorsk reservoir is a natural and technogenic object, the environmental condition of which is determined by the influence of natural factors and anthropogenic pressure connected with the operation of a hydroelectric power station. A change in the composition and concentration of nutrients is one of the indicators of the environmental changes in water bodies. The spatial distribution of biogenic elements (nitrogen and phosphorus) in the ecosystem of the Kharanor reservoir was analyzed by means of complex expedition studies. The content of mineral forms of nitrogen shows seasonal dynamics. At the same time, natural components of nitrogen compounds are modified by the anthropogenic impact on the ecosystem of the reservoir associated with the condition of the river Onon waters and warm water discharged from the state district power station. The highest nitrite content was registered in summer. Seasonal changes of nitrate ions concentration are also characterized by a summer increase and an almost uniform distribution of their content over the reservoir basin with only a slight increase in the area influenced by temperature factors and in the area of the pumping station. From April to October, the seasonal concentration of ammonium ions has a tendency to increase. The highest concentration of total phosphorus in the reservoir water is recorded in summer. In autumn phosphate concentration is lower than in spring. In spring, an increase in total phosphorus is associated with intra-water processes of decomposition of organic matter. The analysis of long-term data on the Kharanorsk reservoir hydrochemical regime proves a tendency of decrease in concentration of such substances as phosphates, total phosphorus, ammonium nitrogen, and increase in the content of nitrates and nitrites. Constant recharge of the Haranor reservoir by the waters of the Onon river results in an accelerated renewal of the water mass, which prevents stabilization of the ecosystem in comparison with other natural reservoirs. In this regard, the observed changes in the concentrations of nutrients are to a greater extent features of external influence than characteristics of a longstanding isolated reservoir.