Abstract. This paper presents the results of a study aimed at determining the possibility of water retention in the lakes located in the upper and middle reaches of the Noteć Zachodnia River in central-west Poland. The study was conducted on the basis of the analysis of available hydrological data and contemporary and archival topographic basemaps. The research was supplemented by a field study from the years 2011-2016, during which numerous surveys and hydrometric measurements were made. Their goal was to determine the natural range of water fluctuations in the lakes under consideration and to identify potential flows in the Noteć Zachodnia River.Observations and calculations allowed the determination of damming ordinates that are within the range of natural water fluctuations of the lakes. On the basis of this information and the previously prepared model of terrain, including the test area, the authors designated zones within the lakes at the required water level and calculated the useful and flood capacity of those water reservoirs. Subsequently, the possibilities of reducing the flood wave on the Noteć Zachodnia River were determined. Calculations were made for 2011, i.e. a year for which the highest winter spate for over 30 years has been documented. It has been shown that, by using only the flood capacities of surveyed lakes, it would be possible to reduce the flood wave on the Noteć Zachodnia River by 30% for the profile closing its catchment below Kamienieckie Lake.The results indicated the validity of damming the lakes located in the catchment of the Noteć Zachodnia River. Water retention in these lakes would restore the water resources in the area and allow reduction of the flood wave during heavy rains. This action would positively affect the ecosystems associated with the river system and would assist the flood protection system in central and west Poland.

The paper refers to the contemporary sensitivity of a ribbon flow-through lake to changeable meteorological conditions (precipitation, evaporation). We checked whether the lake morphology can affect the abrupt changes in hydrological conditions under which environmental changes occur. We analyzed changes in the level and extent of the water table in relation to morphological thresholds of a Charzykowskie Lake. Changes in the lake water level were disproportionate in relation to small changes in the volume of water involved in the exchange. During 55 years of observations, the lake water level did not exceed the threshold values of sensitivity to shortage or surplus stress.