In the last decades, several hydroelectric power stations were constructed in Slovakia which have considerable effect on the fish community of rivers. To reduce their ecological impact, fishways were usually installed at the dams of these stations. Our research aimed to test the fish passage function of the fishway of Hronská Dúbrava small hydroelectric power station, which is located on the River Hron. The aim of this diploma thesis is the observance of the qualitative and quantitative structure of the migrating fish in the fishway. This section of the river is dominated by rheophilic species typical for the barbel fish zone. In order to evaluate the fishway use by local fish community, we carried out trap samplings in the spring of 2017 and we used the data of an electrofishing research performed in 2012 by other researchers. According to these, 16 of the 37 fish species living in this area of the Hron were recorded in the fishway. Among the dominant rheophilic cyprinids, spirlin (Alburnoides bipunctatus), gudgeon (Gobio gobio), chub (Leuciscus cephalus) and dace (Leuciscus leuciscus) were using the fish passage. We evaluated the sex ratio, age and length structure of the most represented species and noticed reasonable differences in the results. Our research points out the importance of examining fishways, not just in Hronská Dúbrava but on every river, that provides information about the effectivity of these facilities and can be useful by the construction or reconstruction of other fishways.