The basis of scientific approach to quality man-agement of water object is mathematical analysis of dependence of the processes of change of water quality arriving on the exit from the reservoir from the quality of water on the entrance to the reservoir cooler. The characteristic of the processes of for-mation of water quality in BGRES-1 reservoir cooler is their dependence on a large number of operated and uncontrollable factors (temperature, time, res-ervoir morphology, hydroweather conditions, the content of ingredients in a river drain, etc.) many of which change stochastically. The results of mathe-matical modeling of relationship between the pa-rameters of water quality of the drain and the re-ceipt of allochtonous, autochthonous biogenous substances under anthropogenous loads of reser-voir cooler ecosystem are presented. Quantitative assessment of the contribution to the change of parameters of water quality of inflow of feeding riv-ers, thermal dumping of power plant, receipts of organic and biogenous substances in water from flooded soils, peat in the course of formation of quality of water of reservoir cooler for long period of time creating scientific base for the forecast of eco-logical condition of reservoirs coolers of nuclear and thermal power plants is made. The basis of scientific approach to quality management of water object is mathematical analysis of dependence of quality of water in the drain from the reservoir from the top part. As a result of researches the following conclusions were drawn: 1) between the properties of water in characteristic areas of water area of reservoir cooler of thermal power plant, on one hand, and in dam area of a drain, on the other hand, there are additive cause and effect depend-ences being solved by mathematical modeling by methods of regression analysis; 2) mathematical modeling can form methodological basis to optimi-zation of water quality of reservoirs coolers of ther-mal power plant for the technological purposes and an aquaculture.