Run-of-river hydropower plants delay or prevent the downstream migration of fish if suitable measures for fish protection and migration are missing. Furthermore, fish can be injured or even killed when passing through the turbine, depending on the type of turbine and operation. So far, there is good empirical data considering the application of horizontal rack systems or vertical rack systems with clear distances of 10 to 20 mm [1], [2]. In the ideal case, they keep the fish away from the turbine inlet and guide them in the direction of a bypass. These systems stand the test mainly at small or medium size plants. At large plants, fine screens are not practicable due to high discharges, technical and operational problems (like clogging, hydraulic losses) as well as high investment and operational costs. At the moment only alternative solutions like “fish-friendly turbines”, operation management adjusted to the downstream fish migration (e.g. passage over the weir, optimized turbine operation) or fish transport systems are a possible solution to the problem [1]. The use of these measures is limited by the location, type of plant and fish species which is why no actual state of the art is available at medium to large scale power plants. There are also major knowledge deficits on the general behaviour of potamodromous fish species and smaller size classes at fish protection and guiding systems [2]. Due to many unanswered questions and the urgent need for action considering the implementation of the European water framework directive, several research groups are dealing with this topic in the German-speaking countries ( [3],[4],[5]).

A state of the art for fish protection and downstream migration in the actual technical discussion at small to medium size hydroelectric plants is considered to be the bar rack bypass systems according to Ebel, Gluch and Kehl. Racks of this kind with 10 mm bar distance have already been realized for discharges of 70 m³/s , a rack length of 50 m and a height of 8 m (Forum Fischschutz und Fischabstieg 2018). This design requires a massive constructional effort and sometimes poses considerable operational efforts. For larger plants no state of the art can be defined so far [6].

The fact that no state of the art is availiable for medium to large scale power plants caused the Unit of Hydraulic Engineering to develop the FishProtector.

Literature