In the master degree thesis, we evaluated the effect of transverse river structures on longitudinal connectivity of rivers and fish in the Sora River basin. At first, the types of transverse river structures with potential impact on fish migration in rivers were defined (weir, dam, rock-ramp, sluice gate, torrential barrier, road culvert). At the investigated Sora River basin we collected data on 150 transverse river structures, including 19 dams, 126 weirs and 5 rock-ramps. Several different methods for priority ranking of transverse river structures in order to improve longitudinal connectivity of rivers were reviewed, and based on the available data and the suitability of the considered methods, we selected the Canadian method. For the Sora River basin we calculated dendritic connectivity index – DCIp index. We also calculated the theoretical DCIp indexes for determination of transverse river structures that have the greatest impact on migration of potamodromous fish. Transverse river structures, higher than 20 cm, were considered as impassable for fish. The result of the DCIp index of the examined Sora River basin showed a high pressure of transverse river structures, impassable for fish. Based on the calculated DCIp index values, we made a priority list of transverse river structures, where the establishment of longitudinal connectivity of rivers for fish needs to be done. Also the solutions for establishment of longitudinal connectivity of rivers for fish were reviewed. In the last part of master degree thesis we covered the Slovenian legislation regarding transverse river structures and longitudinal connectivity of rivers and fish, and further guidance to improve longitudinal
connectivity of rivers was given.