The rivers Lika and Gacka are sinking rivers of the Dinaric karst. Due to their specific characteristics, both rivers need to be studied and analysed, because of a very significant phenomenon in the area through which they flow. Therefore, it was necessary to apply different methodologies which could help in reaching conclusions and defining the studied phenomena in these two neighbouring river basins. While the river Lika is a torrential river, the river Gacka has a highly balanced system thanks to the geographical area, which is confirmed by the data analysed in this thesis. Since for every analysis it is necessary to know the methodology used in data analysis, each methodology is described. These are: basic statistical analysis of data, data series and trends, Gaussian and Gumbel probability distribution, frequency and duration, but also correlation and homogeneity analyses. The data used in the thesis were collected from hydrological stations Izvor Gacke, Pećina, Čovići and Podgora on the river Gacka, and Budak and Sklope reservoir on the river Lika. Data was analysed individually for each station, but comparison of data from stations on the river Gacka and stations on the river Lika was also made. Based on the data from each station, it can be concluded that the spring zones are different; for instance, the Gacka spring and the Pećina spring have been shown as stations with different hydrological data, which can be accounted for by the fact the springs are recharged from different aquifers. Čovići and Podgora are almost identical stations because they have the same hydrological features and consequently similar hydrological data. The analysis has shown that the stations Budak and Sklope reservoir on the river Lika are similar stations, which is supported by the similarity of the analysed data. Having analysed data for each river, an interconnection between these two rivers was also considered, because of assumptions that the river Gacka is recharged from the river Lika. The thesis doesn’t show this assumption to be true, but it doesn’t refute it either. It is certainly necessary to intensify monitoring and analyse data from all the hydrological stations in both basins with as many different methods as possible in order to be able to reach better and more accurate conclusions.