Hydropower plants interrupt the longitudinal connectivity in river networks, which among others hinders downstream fish migration and puts fish passing through turbines or across weirs at risk to sustain considerable injuries. Among other factors, this has led to a decline in fish stocks. For certain fish species, fish guidance racks with adjacent bypass systems are effective fish guiding structures that mitigate such effects. However, especially regarding the bypass, there are open questions related to its design and operation. This project aims at increasing the fish guiding efficiency of such systems by systematic investigations of current bypass designs and development of an innovative bypass for European key umbrella fish species. To reach this goal, first numerical simulations and subsequently etho-hydraulic experiments will be carried out. The fish behavior is analyzed using a video fish tracking system. Finally, recommendations for the design and operation of bypass systems will be given.