Restoration projects normally include creating spawning grounds and increasing diversity for fish juveniles. In rivers which have been dredged removing their natural bed material, gravels and stones can be replaced and over widened channels constricted to create a deeper low flow channel with river banks that support aquatic plants.
Gravel provides spawning habitat for fish, over widened channels have unnaturally shallow water levels and oxygen levels can become very low. Aquatic plants also provide cover for fish and support animals that the fish might feed on.
Larger restoration schemes consist of increasing meandering and restoring flood-plains.
Tributaries, even small brooks have proved to be valuable for reproduction of salmonids as they can have high densities of juveniles. Sediment balance and natural flow regimes are essential for healthy fish.
The whole life cycle of a fish must be considered within restoration schemes.
Return to the Fisheries page or to the restoring river continuity page
Featured case - Longinoja brook
Small tributaries, including some urban brooks, were restored. The restoration of Longinoja brook begun in 2000 by volunteers. In 2006 and 2011 demonstration projects of brook restoration were accomplished.
Stocked sea trout began to migrate back to the brook and first juveniles of natural spawning
were noticed in 2004.
Densities as high as 140 individuals /100 m2
were counted in the restored sites. Even trout juveniles which were stocked in the main stem found the restored brook as a new habitat. Because of natural spawning
in the river and the tributaries stockings of trout could be stopped.
The Vantaanjoki case shows how water quality and removal of obstacles is the basis for fish stock enhancement. Rivers and brooks even in urban surroundings can contribute to saving vulnerable fish stocks. Cooperation of authorities and volunteers in river restoration increase the value of small brooks for juvenile production and urban environment.
Longinoja brook with high density of trout juveniles (J.Jormola)