The survey examined various restoration options and assessed their feasibility, costs, and disadvantages and risks. To improve fish migration, the survey explored, among other things, improving the performance of the existing fish pass, the possibility of enabling migration past the Merikoski bridges and the ornamental dam weirs, and opening a new migration route through the Hupisaaret streams via a natural fish pass. The survey assessed the risks that the measures may pose to dam safety and, for example, problems caused by ice formation in the fish pass or the ornamental pool. In addition, it assessed the impacts of the diverted flow on Oulun Energia’s energy production.

Based on implementation and/or cost, the alternatives were classified as easy, challenging, or unfeasible.

• Seabed restoration in the Hartaanselkä area to improve fish breeding grounds and rehabilitating the Kissakoski area were identified as easy measures.
• A more challenging measure is to replace the weirs beneath the Tuira bridges with rapids, which would enable fish to access the ornamental pool more easily. For the fish, the best migration route would be via Tuiranväylä.
• Opening a migration route from the Hupisaaret Islands to upstream of the dam was found to be a costly and difficult option due to the existing weir. 

As one of the restoration alternatives, the survey explored directing a continuous year-round flow into the ornamental pool. In practice, diverting water volumes sufficient to support fish reproduction, for example, would necessitate building separate flow regulation and control structures. The design of the environmental flow took into account the power plant permits, required modifications to structures and existing infrastructure, and any necessary zoning amendments and heritage considerations.

See the final report of the survey in more detail here (only in finnish).  

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

The City of Oulu and Oulun Energia are now planning and examining in more detail the restoration measures highlighted in the report.

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. The assessment examines, among other things, the required shoreline erosion protection, modifications resulting from rising water levels, floodwater management, and the impact of the measures on the Merikoski bridge plans. The survey will also enable more detailed cost estimates for the various alternatives. The work is expected to be completed by the end of 2025.

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.

In addition, Oulun Energia is planning measures to prevent fish from getting stuck in the basins under the dam. The bed of the dam channel will be laser-scanned, and based on the results, the rock surface will be treated and water will be drained from the depressions into the fish pass channel. This reduces the risk of fish getting stuck and in the future, fish will be guided to the fish pass more effectively than before. The alteration work is scheduled for late autumn or early winter, following the closure of the fish pass, if weather and safety conditions permit.