Downstream passage facilities with signals that are understood by fish

Barbel in front of the guidance screen (Photo: Armin Peter) - Europe still has barely any downstream passage facilities that guide fish past the turbines of run-of-river power stations unharmed. Now, an interdisciplinary team of engineers from ETH Zurich and fish biologists from Eawag have developed a rack that uses pressure and flow differences to guide fish out of the main flow and into the safe fish passage. Laboratory tests have shown that the system, which works by influencing fish behaviour, is particularly effective for cyprinid fish and salmon parr. For over 100 years, fish ladders have been fitted to hydro-electric plants and other obstacles in order to assist migrating fish, but there is a distinct lack of downstream passage facilities that actually work in practice. The reason for this is that, because fish follow the strongest flow, they struggle to find the weak flow that leads to the safe bypass. As a result, most of them end up in the turbines of the power station along with the main flow, resulting in injury or death - especially in the case of large fish and eels, which are particularly long. Trouts scanning the flow at the rack.