Determined concentrations of BTEX and PAHs in bottom sediments of strong polluted dam- reservoir Dzierżno Duże (Western Part of Upper Silesian Region in South of Poland) are presented. Hydrocarbons (PAH) concentrations have not grown since 1979. The effect of adaptation process of microbiological groups to PAH degradation over the long period of pollution in the anthropogenic ecosystem is presented. Organic pollutants are deposited in the bottom of the Kłodnica river estuary. Total PAHs concentration in bottom sediments was estimated about 30 mg/kg dry weight near the Kłodnica estuary and it gradually decreases. In the distance of 700 m from first part of the water reservoir, PAH concentration is lower than 80% of the concentration, which was determined in the first sampling points of the estuary. In the present ecosystem the hydrocarbons are the element of strong environmental contamination.