Fish passes

The sea trout and other migratory fish swim upstream to their spawning grounds, which are often found in the headwaters of rivers. While dams and other barriers hinder the passage of the fish, there are ways of bypassing them.

A series of concrete basins along the slope beside a hydropower plant dam is a very common solution. The salmon and the trout are good swimmers and adept at slipping through these fish passes even against a strong flow.

Fish locks have also been built, which are not unlike canal locks intended for boaters, and special fish lifts have been used in Finland. All these technical solutions have their limitations; they may not be suitable for all fish species, and they usually are open only part of the time.

Nature-like fishways are today opted for whenever possible. They can be built with natural stones and designed to meander along the slope like a natural brook. Plenty of space needs to be reserved for them, ensuring that the channel is not too steep.

A nature-like fishway usually works well and is suitable for all fish species. Suitable sites for spawning and juveniles can also be prepared in the channel. Not only fish but also benthic animals and such species as the white-throated dipper and the otter feel at home in these channels that resemble brooks. These kinds of fishways become a natural part of the landscape and liven up an urban environment, in particular.