Sixteen polycyclic arom. hydrocarbons (PAH) were biodecompd. in bottom sediments for 150 days with CaO2 as the oxidn. agent both under laboratory conditions (CaO2 dosis 300 g/m(2)) and in 2 metal chambers (CaO2 doses 200 and 100 g/m(2)) located in the Rybnik water basin. The degree of overall removal of the PAHs after 150 days was 83%, 68% and 60%, resp. The concn. of fluoranthene (the most dominant PAH) decreased in the laboratory tests from 13 mg/kg down to about 3 mg/kg (dry mass) after 15 days of the expt. In the chamber tests, the concn. decreased down to 6-8 mg/kg (dry mass) after 30 days. The decompn. kinetics was described with the 2-nd order equation. Fundamentals of the process were also outlined.