In recent years there has been a significant decrease in abundance and species diversity of migrating fish. A significant decrease was recorded especially in diadromous fish species such as Atlantic salmon (Salmo salar) and eel (Anquilla anquilla). A significant population decline was also observed in potamodromous abundant fish species. Transverse barrier which prevents fish migration in rivers and impaired water quality are considered as the main causes of this situation. At present there is being improved a surface water quality, habitat rehabilitation and restoration of the possibility of free migration of aquatic animals. Design and construction of fish ladders are the most important factors to improve conditions of the fish migration. Closely related to this is a migration permeability testing of these fish ladders while the biological function and the activity of a single technical solution is evaluated. A non-invasive automatic monitoring method using a bioscanner Riverwatcher was selected to assess the functionality of fish passage on the river Ohře in Kynšperk nad Ohří. Bio scanner was installed at the end of the track of fish passage. Riverwatcher camera system, a product of Vaki Aquaculture Systems Ltd., was used in the Czech Republic for the very first time. Direct catches of fish samples in the river using an electric unit (section under fishway) were also used for the data collection. Size and species selectivity was tested at the fish ladder. The influence of external factors affecting the course of migration, such as flow rate, water temperature and light, was monitored at the same time.