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.