UPM-Kymmene Oyj: UPM's stream water program brings results - endangered lake-migrating brown trout returned to spawn in Arvajankoski

(UPM, Helsinki, 10 February 2025 at 12:00 EET) - In 2022, UPM carried out the restoration of the rapids area of Arvajankoski, Jämsä, in cooperation with local operators. Last autumn, a monitoring survey by the Central Finland Water and Environment Association found some young-of-the-year brown trout and a spawning nest in the area. This means that natural reproduction of trout has started in Arvajankoski.

Jukka Syrjänen and Niko Kylliäinen from the Central Finland Water and Environment Association conducting a survey on spawning nests at Arvajankoski in 2023.

"It is great news that the restoration has brought results so soon after its completion and the lake-migrating brown trout have returned to spawn in Arvajankoski. The status of the migratory trout in Päijänne water system is currently poor and we expect that the restoration of Arvaja will improve the situation. It is at least a promising start," says Mikael Rytkönen, Environmental Manager at UPM Energy.

The restoration of Arvajankoski in Jämsä was completed in October 2022. The project involved demolishing the old dam and building a mirror dam on the rapids. In addition, the old fishway was replaced by a natural fishway and new spawning and nursery areas were formed in the area. A fishway will allow fish to go upstream of the rapids and a mirror dam will smooth out the fluctuations in the surface level. The aim was to restore the rapids' stream ecosystem and open the Arvaja rapids route to endangered lake-migrating brown trout and other species.

Last autumn, researchers from the Central Finland Water and Environment Association found one spawning nest in Arvajankoski, located in the neck of the area that had been restored as a spawning and nursery habitat. In addition, 0-year-old parr were found in an electrofishing survey. The surveys found no evidence of egg-laying or juvenile stocking in the Arvajankoski, so it is likely that the spawning nest was missed in the previous winter's spawning census. It is often difficult to detect spawning nests in fresh restoration gravel.

"The site of the spawning nest found in autumn 2024 has little gravel or stones to protect the nest. It might be even more suitable as a spawning area for trout if an additional small-scale restoration of the area was carried out, like adding gravel and large stones," says Tuomo Laitinen, Executive Director of the Central Finland Water and Environment Association.

For more than 40 years, the parr density of the wild trout population has been monitored annually in the rapids of the Arvaja watercourse. The survey has now been continued thanks to funding from UPM's stream water program, and Arvajankoski has been included as a new site in the study in 2023.

The restoration of Arvajankoski was completed in 2022.

There are around 5,000 structures classified as dams in Finland, the vast majority of which are meaningless for energy production. There are about 220 hydropower plants and their dams in Finland. UPM's stream water program aims to restore or release 500 kilometers of stream water by 2030. The program promotes biodiversity by, for example, removing unnecessary migration barriers such as dams, replacing road culverts, and restoring rapids and streams. We are also participating in various pilot and research projects in cooperation with various stakeholders, such as local expert organizations, companies, and ELY centers.

For further information please contact:
Mikael Rytkönen, Environmental Manager and Coordinator of UPM's Stream Water Program, UPM Energy, tel. +358 40 826 3636
Tuomo Laitinen, Executive Director of Central Finland Water and Environment Association, tel. +358 400 614273

UPM, Media Relations
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tel. +358 40 588 3284
media@upm.com

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