Summary:

The scientific research of the oxbow lake of Słupia River was carried out from 1998 as a preparation for drilling the conception of renaturyzation of Słupia River. It consisted in including particular oxbow lake in the right stream. The research included the analysis of the most important ecological formations with special regard to periphyton living in artificial and biotic substratum. In 2003 Koński Staw, one of the oxbow lake in the lagoon polder of the city of Słupsk, was submitted to the process of dredged. Drainage works created new life conditions for hybrobionts. During the research period (2004–2005) the density of bottom microfauna was increasing noticeably. The density of zooperiphyton living in artificial substratum was also increasing from 132 to 303 thou. indiv. m^-2. However, high fluctuation on the biotic substratum could be observed. The density of zooplankton was fluctuating between 9.3 – 15.8 thou. indiv. per dm^-3. The results of the research allow to state that the drainage works carried out in the oxbows lake of Słupia River are very profitable for zoocoenoses hybrobints. The removal of bottom sediments with hydrogen sulphide accumulated in reservoirs caused the reconstruction of qualitatively- quantitative structure of macrozoobenthos, zooperiphyton and zooplankton. It allowed to verify the original draft of the renaturization plan by including dredged oxbows, where representatives of ichtiofauna may exist. The cleaning process of river waters can be carried out thanks to lichen formation enriched with filters and sedimentators.