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The fish pass in numbers

The Merikoski fish pass was built in the summer of 2003, and it is the most visible part of our environmental work related to fish. Throughout its existence, the fish pass has, for the most part, worked well. Over all, almost 16,000 salmon and more than 3,000 trout have swum upstream along the fish pass.

Construction was preceded by years of extensive research. The research looked for and found a suitable place for the opening and looked at the upstream migration behaviour of different fish species over an experimental ladder and in the water mirror covering the rocks of the former riverbed.

The longest fish pass in Finland

  • Length 750 metres
  • 64 stairs
  • Width 2.8–7 metres
  • Depth approx. 2 metres
  • Ascension 11 metres
  • Flow 1.2–2 m3/sec.
  • Costs EUR 1.2 million

Research data on migratory fish

The functioning of the Merikoski fish pass has been studied over the years together with the Natural Resources Institute Finland. There is still room for improvement in terms of increasing the number of fish that swim upstream along the fish pass. It would also be desirable for salmon to enter the river earlier and find the fish pass without a long delay.

Movement along the fish pass is monitored constantly. At the end of the pass, there is an observation room where, through the aquarium glass, it is possible to observe the movements of the fish. There is a webcam directed at this window. A new fish counter was installed at the end of the fish pass in 2018. All fish entering the river through the fish pass is videotaped, which is the basis for determining the quantities, species, length, weight, and possibly also the gender of the fish coming through.

According to the statistics, migratory fish swimming upstream has included not only salmon but also trout, perch, bream, and roach. A few whitefish and graylings have also come through the fish pass. Based on the information received from the calculator, it is known, for example, that the biggest fish that have passed through the fish pass has been an 18,2 kg salmon (August 8, 2023) and a 7,2 kg trout (September 18, 2023) and that the busiest day at the fish pass was 12 September 2019, when 245 salmon swam upstream in one day.

The visitor of the year 2022 was an 89 cm long otter (May 25, 2022).


Fish pass salmon run

We will update the monthly fish migration data for the current year in the table. The daily statistics for the previous year can be found in the appendix below the table. A new fish counter was installed for the fish pass in June 2018.

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Statistics on fish