Barriers to migration cut off streams

Fish and many other aquatic organisms can only move from one place to another through water. If they come across a dam or inexpertly installed culvert, their journey stops there. This happens quite frequently in our streams and rivers.

There are more than 5,000 dams in Finnish rivers and streams, and the number of other barriers to migration is even higher. It has been estimated that approx. 90,000 culverts providing access across a water body have been installed in our road network, and up to one third of them may prevent the movements of fish and other aquatic organisms. In addition, water bodies contain old mills and timber floating structures, bottom weirs and other barriers.

All of the largest rivers in Finland have been dammed, with the exception of the border rivers Torne and Tana. A large part of natural salmon and trout populations in large river systems have been lost because of dams, and barriers to migration have still not been removed. While the few fish passes built to bypass dams help fish migrations, designing well-functioning fish passes has proved difficult, and not enough attention has been paid to enabling downstream migrations. Efforts are currently being made in many places to build nature-like fishways that provide a passageway for all fish species and, in the best case, create new stream habitats.

Most smaller rivers have also been dammed. Dams have been built for different purposes: for water regulation, flood protection and hydropower generation. There are more than 500 hydropower plants that only provide electricity for domestic use. Most power plants connected to the national grid are mini or small plants with a capacity of less than 10 megawatts. The goal is to dismantle dams which, while having little or no significance for electricity production, have a major impact on the status of the aquatic environment.

Smaller barriers to migration are removed in connection with brook restoration projects. However, thousands of small water bodies and ditches are not within the scope of such projects.