The results of the first (since 1939) hydrochemical investigations of Gliwice Channel have been presented. The polluted K.lodnica River affects bad water quality of the canal. For example the concentrations of chlorides (Cl), sulfates (S04), sodium (Na), potassium (K), conductivity and dissolved substances quality of water is out of standards. In the case of BOD and COD the water quality is changed from out of classes to II class. pH and oxygen concentration are in I class. Although no salinity waters flow into the canal, the water quality get improved slightly only. The decrease of pollutants concentration is related to theirs dispersion. In the case of water quality the self-purification processes are of secondary importance.

This study includes hydrologie characteristics of the Potok Toszecki basin area and the results of chemical analysis of water quality of the Potok Toszecki. These investigations were carried out in following periods: from March 1993 till May 1994 and from January 1997 till June 1998. The results of investigations on the chemical parameters of water quality were compared with analysis, carried out in 1976. Under the results of this investigations water quality of the Potok Toszecki - a watercourse, which flows to the Pławniowice Reservoir - was defined and essential factors, connected with character of the basin area have been shown. Classification of several parameters was achieved under the official decree of the ministry of environmental protection from November 5th 1991. On the basis of this classification it was found, that the main risk for the Pławniowice Reservoir are biogenie substances and suspension, inflowing to the Reservoir together with the water of the Potok Toszecki. Improvement of the existing situation will be possible only if firm waste-water managements action will be taken.