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, approximately 16,000 salmon and more than 3,000 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, will conduct a study in 2024 to evaluate the feasibility of the various objectives concerning the Merikoski area. The project will be completed at the end of the year. Following this, we will be able to see which biodiversity measures can be implemented quickly, which require extended planning and execution, and which are deemed unfeasible for one reason or another.
Flow testing as part of the study
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.