Abstract: The Klimkówka Dam Reservoir is situated on the Ropa River in southern Poland. The surface area of the reservoir is about 306 ha and its capacity is 43.5 hm³. Acoustic surveys were conducted both in the daytime and at night using a SIMRAD EY-500 split beam 120kHz echo sounder. Maps of the spatial distribution and density of fish were drawn up, and the fish species structure, size, number and biomass were estimated based on acoustic surveys and supervised net catches. The highest fish density at night occurred in the river tributary zones (836 fish/ha). In this area at night fish density was twice as high as in the central region of the reservoir. The density figure for the whole reservoir was 638 fish/ha and was 1.4 limes higher than that in the Solina Reservoir and from ten- to twenty-fold lower than in several other studied lakes. Fish catches performed with pelagic trawIs and net sets revealed the presence of nine fish species. Lake and river trout species which had been introduced to the reservoir were not noted. The fish biomass was estimated to be 11.5 tons, or 44.4 kg/ha, and was from three to 14 times lower in comparison to the estimated figure in several other lakes.