Research of polar lakes helps to obtain a new in information about limnic process in Polar Regions. It is well known - that these areas are most sensitive to climate change, and therefore even a small shift of the important parameters in aquatic environments can play a huge role for water ecosystems. The thermic regime of polar lakes has its own peculiarities. The water temperature variability in polar lakes usually ranges between 0 and 18 °C , the icecover thickness can reach up to 2 m. The freeze-up usually occurs in the first month of autumn, the breaking up of ice starts beginning of June. Current studies present the particularities of the thermokarst lakes and their thermic regime. The thermal regime was modelled using the thermohydrodynamic model “Flake” developed by Russian – German research team (www.lakemodel.net). Input data for this model are meteorological characteristics as well as lake morphometric measurements. Except climatic parameters what else is the thermic regime of lakes affected by? In our opinion, the heat turnover in the lacustrine sediments of the lake is one of the important processes that can give an additional thermic information. Lacustrine sediments represent a specific bottom “sediment chuck” between lake water body and a depression. Sediment properties such as thickness, humidity, grain-size, organic content and geochemical composition, significantly determine the physical characteristics that influence the lacustrine thermal regime. The thickness of the lacustrine bottom sediment is one of the important characteristics for lake thermal regime modeling, especially in the lakes of the Arctic permafrost regions . This parameter is included in the aforementioned thermodynamic model. Numerical experiments were conducted to test the impact of sediment thickness on the thermal regime. Thickness of the lacustrine sediments were varied from 1 m to 5 m. Modeled results show that the dynamics of the thermic fluxes were similar for sediments with thicknesses of 3 m and 5 m. The maximum positive heat flux was calculated for a thickness of 3 m. The highest negative thermic flux was calculated for a sediment thickness of 1 m. In deep reservoirs, bottom sediments significantly slow down the freezing of the reservoir, since heat accumulates during the summer period. Other physical characteristics of bottom sediments also affect the thermal regime of lakes. For example, wet bottom sediments warm slower because of their low heat capacity. The destruction of organic matter in the water also influences the thermal regime. Heat flow from the organic matter decomposition in sediments, can be quite significant. In the framework of this study, the mechanisms heat flow in lacustrine bottom sediments are analyzed and their parameterization in thermic modeling tested.