Thermal pollution of water bodies is an unavoidable consequence of thermal or nuclear power plant operation. To minimize the detrimental effects of these plants, one should assess the nature of dangerous zones. The most effective approach to solving these problems is the computational experiment. This paper presents the results of a numerical study of thermal pollution in one of the largest thermal power plants of Europe - Permskaya TPP, using the Kama Reservoir as a natural cooling system. Such problems are traditionally solved in 2D formulation using the "shallow water" approximation. However, with this approach it is impossible to take into account the vertical inhomogeneity of the temperature field. On the other hand, 3D models, which can take into account the effect of density stratification, require very large computational resources. In this work, a combined approach, based on a combination of computational models in the 1D, 2D and 3D formulations, is applied. (C) 2018 Elsevier Ltd. All rights reserved.