In the municipality of Salo in Southwest Finland, the river Kiskonjoki is an important river for migratory fish. Removing the Holstenkoski dam will expand the habitat for fish and other stream-dwelling organisms. Over 40 kilometres of open stream and river areas are now accessible to fish. Diverse species need freely flowing waters, which benefit not only fish but also otters and mussels. The free-flowing water also increases the area’s tourism potential, vitality, and biodiversity in general.
The Holstenkoski dam received the necessary permits in May 2023, and in spring 2024, a 12-meter section of the dam was removed. Dredging work was also completed in the spring, and the channel above the dam has now been restored to its original state. Restoration work will be finalised in August after the bird nesting season. An official opening ceremony is scheduled for September.
The project’s main partners are private local land and water area owners who have supported the initiative. The main funding for the project comes from the Ministry of Agriculture and Forestry’s Migratory Fish Population Rehabilitation Program, NOUSU. The project has also received funding from the Open Rivers Foundation, WWF Finland, the Raija and Ossi Tuuliainen Foundation, the City of Salo, Valonia, Lake Kiskonjärvi of Kisko Water Management Association, the Southwest Finland Fisheries Area, and the Southwest Finland Nature Conservation District are also supporting the project through co-financing.
During the project’s preparation, the fisheries services of the Southwest Finland ELY Centre, City of Salo, and the Turku Provincial Museum collaborated long-term. Archaeological surveys were conducted in the rapid area to ensure that valuable cultural-historical sites were considered in the restoration efforts.
Holstenkoski is in the River Aneriojoki, part of the Kiskonjoki-Perniönjoki watercourse that flows into the Archipelago Sea, a part of the Baltic Sea. It is a nationally significant migratory fish river protected by the Rapids Protection Act. The Kiskonjoki-Perniönjoki watercourse watershed hosts an original sea trout population, including Atlantic salmon, migratory whitefish, and vimba. In 2022, fishways were completed at Koskenkoski and Hålldamm in the Kiskonjoki. These fishways provide migratory fish with free passage to Kisko Church Lake and the headwaters of the watershed flowing into it.
As the climate changes, the importance of free water routes may become even more pronounced. It will be increasingly important for fish and other aquatic organisms to access small, cool, groundwater-influenced streams and rivers. The headwaters of the Kiskonjoki-Perniönjoki watercourse watershed and the Varesjoki River are in the valuable Hyyppäränharju area, which has many valuable and threatened habitat types, extensive groundwater areas and groundwater-influenced stream waters.
