The aim of the present work was to analyse the results of investigations on the heavy metals content in the water of the Nakło-Chechło Reservoir. In this study the importance of this element in the characteristic of aquatic environment is stressed. Small content of heavy metals has excluded the possibility of the discharge of municipal and industrial sewage. All of these toxic substance included in water have confirmed that the Nakło- Chechło Reservoir is under strong hydrological and chemical influence of the precipitation and surface run off from the Reservoir basin area.

The paper presents the conversion dynamics of basic nitrogen and phosphorus forms as main factors initiating eutrophication process in Naklo-Chechlo reservoir. Limnological investigations of recreation reservoir were carried out in the period from January to December 1996. The results of chemical analyses of water samples taken in two collecting points of the reservoir and a composition of surface run-off from the basin area, have been presented.

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.

In the presented work the limnological characteristics of the Reservoir Nakło-Chechło elaborated on the basis of investigations carried out in 1996 has been shown. The results of investigations on thermal and oxygenic conditions existing in the Reservoir and the change dynamics of selected physico-chemical indicators of water quality in the Reservoir Nakło-Chechło are described. The paper describes aspecific example of acidotrophy of the Nakło-Chechło Reservoir as a result of anthropopressure. The results of chemical analysis of water in the Nakło-Chechło Reservoir and evaluation of the dynamic changes of various indicators with the atmospheric precipitation quantity on the basin superficies have shown that the Reservoir is under strong hydrological and chemical influence of the precipitation, which generally is acidic and has a very low total hardness. The exceptional vulnerability for acidification due to deficiency in water buffering capacity was, however, the decisive factor. The discharged weak buffering capacity of the Reservoir water facilitates the influence of direct precipitation and through superficial run off. The results of chemical analysis show high state of water quality in the Reservoir Nakło-Chechło as regards amount of indicators which describe water mineralization degree.