EN
For assessment of the organic matter mobility rate, dissolved and particulate organic carbon were used. Quality of the organic matter was determined on the grounds of the relative indicator of aromatic properties (SUVA260) and the absorbance ratio at 260 nm (A260) and 330 nm (A330). The study has revealed that the dominant form of organic carbon is the dissolved form (DOC). The main source of organic matter is the autochthonous production, intensifying in spring, which is exhibited by the growth of the heterotrophic bacteria number and intensive phytoplankton bloom. Organic matter in the lake is transferred both spatially and vertically. The rate of these processes is determined by, respectively: forced water flow resulting from the cooling waters dump and sedimentation of organic matter on organic and inorganic suspensions, which is favoured by the carbonate-calcareous character of the Lake Mikorzyńskie waters. Organic matter adsorption to calcium carbonate and destruction running with the heterotrophic bacteria participation are one of the major factors limiting the heavy degradation of the lake waters.