Fish and lamprey passage in a combined Denil and vertical slot fishway

A fishway (fish pass), consisting of vertical slot and Denil sections, was constructed at the lowest dam on the River Kemijoki, northern Finland, in 1993. The river was one of the best salmon rivers in Europe until 1949, when the dam and the hydropower plant were completed close to the river mouth. From 1993 to 1995, nearly 1000 adult salmonids passed through the fishway despite heavy fishing below the dam. Of environmental variables measured, water temperature, headwater level, and discharge through the power plant in relation to season changes explained most of the variation in Baltic salmon, Salmo salar L., numbers. They had a minor effect on trout, Salmo trutta L. Migratory whitefish, Coregonus lavaretus (L.), entered the fishway but were not observed in its uppermost pool. River lamprey, Lampetra fluviatilis (L.), passed through the vertical slot section of the fishway after plastic bristles were fastened into the bottom of the slots.     

Atlantic salmon, Salmo salar L., and sea trout, Salmo trutta L., passage in a regulated northern river – fishway efficiency, fish entrance and environmental factors

The number and the size of Atlantic salmon, Salmo salar L., using the Isohaara fishway was elevated by increasing the fishway discharge and by changing the type of the pass entrance. The fishway is intended to help fish bypass a hydroelectric station located close to the mouth of the large, regulated River Kemijoki, in northern Finland. Multi-sea-winter (MSW) salmon returned to the river mouth during peak flows in early June but did not use the fishway until 1 month later. Their number in the fishway was positively correlated with the tailwater level. One-sea winter (1-SW) salmon, which arrived approximately one month later, started to enter the fishway without corresponding delays. In autumn, a high tailwater level and a small drop at the fish entrance seemed to be needed for the successful passage of these small-sized salmon and sea trout, Salmo trutta L.