Despite technical innovations in hydropower being limited, the potential for hydropower development in the EU maintains a prominent position amongst renewables. However, it affects the essential characteristics of aquatic habitats supporting fishes’ biological functions, such as reproduction by blocking or delaying fish spawning migration. Hence, hydropower industry address fish migration issues by fish passage facilities, among others. To ensure great effectiveness of these measures, ecological knowledge and decision support tools are essential. In this study we customize a modelling tool to enhance the efficiency of fish passes by assessing and modelling the attraction flow and upstream fish migration. Specifically, the agent-based model is developed based on detailed fish tracks observed in the turbulent outflow area around 200 m downstream of a fish ladder bypassing one of 5 hydropower plants on the river Iller. The 2-dimensional fish tracks were collected using the VEMCO positioning system with HR2 180 kHz receivers and fish tags transmitting an unique acoustic signal every second. Beside detailed fish movements in the head stream, fish presence and the catch efficiency of the temporary catch construction in the fish ladder was assessed. Specifically, movements of 25 grayling (Thymallus thymallus) and 25 barbel (Barbus barbus) were accurately observed. Tagging of fish caught in the head stream, as well as fish caught in the fish ladder allowed to assess potential effects of learning behaviour on the efficiency of finding the fish ladder entrance. The study is rare in its kind, because high frequency acoustic telemetry allowed positioning tagged fish every 1 to 3 meters in a turbulent area direct downstream of a hydropower plant.