The City of Espoo and HSY restore fish migration routes – important for endangered trout and other aquatic life
The City of Espoo and the Helsinki Region Environmental Services Authority (HSY) have implemented a joint project to restore fish migration routes in Espoo. The project supports the biodiversity of aquatic environments and restores fish migration routes of endangered trout and other species.
Alterations made in a joint project now enable trout and other fish to climb from the sea into Espoo’s inland waters. A new fishway was built in the north-eastern part of the Dämman reservoir and an obstructing barrage in Lake Pitkäjärvi in Nuuksio was replaced with a new submerged weir, allowing trout and other fish to climb up the Mankinjoki river basin all the way to the Dämman reservoir and Lake Pitkäjärvi in Nuuksio.
The fishway opens a route to Espoo’s inland waters
The new Dämman fishway allows fish to bypass a dam that has previously obstructed their migration. The fishway is approximately 175 metres long, consisting of 34 rock ramps and the pools that form between them. Fish can rest in the pools before continuing their journey. The pools between the ramps are approximately four metres in length, and water level rises about 20 centimetres with each ramp. A larger resting pool is formed slightly before the middle of the fishway.
With the obstructions removed, fish can now freely enter Espoo’s inland waters. This is particularly important for the reproduction of trout, an endangered species of fish. The project improves the reproduction and living conditions of the trout population.
The project promotes the implementation of the national fish passage strategy and is in accordance with Uusimaa’s water management action plan for 2022–2027 and the action plan for water protection in Espoo for the years 2022–2027.
The project improves aquatic biodiversity and benefits outdoor activities
Development projects for water bodies are an important step towards more sustainable water management. They demonstrate how biodiversity can be promoted through practical actions. The protection of biodiversity, particularly from harm caused by human activities, is essential for preserving nature for future generations.
Migratory fish are not the only ones that benefit from these projects. Restoring waters closer to their natural state also benefits other fish and aquatic life that live in running water. Restored waters also provide people with more varied ways to enjoy nature. Areas with diverse aquatic life and ecosystems have more recreational value and are more attractive for outdoor activities.
- Although HSY’s activities, such as construction and water regulation, inevitably impact the environment, we always try to reduce harmful effects and to develop solutions that support biodiversity in the long term. The construction of fishways and the removal of obstructions to migration are concrete examples of how we can promote the recovery of aquatic life, Director of Division Veli-Pekka Vuorilehto explains.
- For the City of Espoo, the removal of obstacles to fish migration in Dämman and Lake Pitkäjärvi in Nuuksio is a follow-up to the fishway of Gumböle mill dam, which was built in the Gumbölenjoki river in 2020. After the completion of the fishway in Gumböle, recently hatched young trout have been found above the mill dam during electrofishing tests every year since 2021, explains Mira Heiskanen, Environmental Technology Engineer at the City of Espoo.
Many years of close cooperation
HSY launched the planning of the fishway in November 2014. Amending the regulations at Dämman became necessary after the waterworks facility was decommissioned. The planning period lasted for multiple years and included a preliminary survey, a regulation amendment plan, a general plan and an application plan in accordance with the Water Act. The project’s permit process began in 2020 and ended with a permit decision at the end of 2022. After a long preparation phase and construction, the fishway was completed in autumn 2025.
The project involved close and successful cooperation with experts from the Uusimaa Centre for Economic Development, Transport and the Environment. The project received funding for the construction of the Dämman fishway from the Southwest Finland Centre for Economic Development, Transport and the Environment. For the work at Lake Pitkäjärvi in Nuuksio, the project received funding from the Uusimaa Centre for Economic Development, Transport and the Environment. The site was designed by FCG Rakennettu Ympäristö Oy.
Cooperation between HSY and the City of Espoo will continue at Lake Bodom with the alteration of a barrage and the construction of a fishway. This cooperation will remove an obstruction to trout migration into Lake Bodom in the Espoonjoki river basin. The work is expected to be completed in 2026.
