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Merikoski dam and Merikoski bridges photographed from an aerial point of view.
Channel of Merikoski photographed from air in may 2024.
Breadcrumbs

Development of the Merikoski area

The construction of the Merikoski power plant in the 1940s closed the lower part of the Oulujoki river catchment area with a dam. The construction of the hydroelectric power plant had a significant impact on aquatic organisms and especially on migratory fish. The Merikoski dam obstructed fish migration to the Oulujoki river and resulted in the destruction of the breeding grounds upstream during its construction. Flow regulation and alterations affect ecosystems by limiting the natural fluctuations in water levels.

The Merikoski area has been actively developed for more than 20 years. The fish pass bypassing the Merikoski power plant was completed in 2003. Over the years, over 18,000 salmon and almost 4,000 trout have migrated to the Oulujoki river through the fish pass. 

In 2021, a preliminary assessment was completed on the technical feasibility and costs of the fisheries restoration proposals for the Oulujoki river (Sweco 2021). This assessment evaluated the potential for reintroducing water to the old Merikoski river channel and examined the prospects for fish reproduction in the area.

The Oulujoki waterways vision and areas identified for further study

The Oulujoki watercourse vision, completed in 2023, identified several key areas for further study, including developing the existing fish pass, examining the natural fish pass, implementing year-round flow in the old river channel and the related construction of a small-scale hydroelectric plant, developing the Hupisaaret area, and improving breeding opportunities for Hartaanselkä whitefish.

The City of Oulu, in collaboration with Oulun Energia, Fortum and the North Ostrobothnia Centre for Economic Development, Transport and the Environment, started a study in 2024 to evaluate the feasibility of the various objectives concerning the Merikoski area. 

In May 2024, Oulun Energia conducted a flow test on the Merikoski dam channel as part of the development work. During the flow test, the Merikoski dam bridge gates were opened on three days, and water flow in the area was monitored at three different flow rates. At the same time, the optimal water flow levels for environmental purposes to determine their potential positive impacts on local aquatic organisms. Water flows were monitored using an aerial drone and by direct observation from the shore.

The project completed at the end of 2025 when the the final report was published (only in finnish).

 

Restoration measures are now being designed in line with the evaluations made in the survey

As a continuation of the study work and its final report, a more detailed investigation was launched at the end of 2025 by the City of Oulu and Oulun Energia. 
 
The City of Oulu has continued to examine the restoration proposals presented in the preliminary survey by commissioning a more detailed feasibility and risk assessment of the water management options.
 
Oulun Energia is investigating possibilities for directing water to the dam channel from the power plant dam on a year-round basis. The survey examines various options for implementing the discharge structures. It includes a preliminary hydraulic design for the water intake opening, an examination of the structures and equipment to be dismantled and replaced, as well as the necessary permits. The survey also evaluates the risks related to the project’s technical feasibility, dam safety, and gate operation. Preliminary cost estimates will be made at the same time.  Another alternative being explored is improving the performance of the fish pass to increase the number of fish passing over the dam.
 
More detailed information on the study of remedial measures is available in a related news article.