Objective: Development of a system of models describing the processes of heat and mass transfer in the “catchment – watercourse – reservoir” system and enabling the assessment of the impact of economic activity and climate change on the state of bodies of water. Methods: A water system model is configured using the newly developed and working models of processes in accordance with the determining factors: 1) the requirements of the task; 2) structural features of the research object; 3) the presence and locations of the observation network points as a source of input information for modeling. Results: The resultant system of models includes seven deterministic and one stochastic models. The deterministic models are the model of water runoff from the catchment ILHM, model of chemicals removal from the catchment ILLM, model of water flow, sediment transport and dissolved impurities in an open channel (1D, 2D, 3D), 1D model of reservoir’s thermal regime and mixing FLake, 1D model of non-conservative impurity dynamics in reservoir FLakeEco, 2D model of currents and sediment transport in a shallow reservoir, 3D model of heat and mass transfer in reservoir. The stochastic component of the system is the SWM weather model, which is a stochastic generator of meteorological elements.