When the waterway was opened at Okome Mill in Stockån, fish were able to move freely upstream through the water system. Spawning salmon have been observed—and the restoration could have a major impact on the critically endangered sea lamprey, eel, and other species. Watch our video clip from our visit to the restored area.
The Stockån is a tributary of the Högvadsån and the River Ätran. For some time now, extensive work has been underway to restore the river’s aquatic environments. At Okome Mill, a dam has been removed, and the water can now flow freely.
Elisabeth Thysell, a biologist at the Halland County Administrative Board, sees significant environmental benefits.
Photo: Nicka Hellenberg
“The open waterway allows several fish species to migrate upstream into the system. Among the species that benefit are salmon, eel, and the critically endangered sea lamprey,” says Elisabeth Thysell of the Halland County Administrative Board in the interview.
The results have come quickly. Spawning salmon were seen almost immediately upstream of the former migration barrier. Elisabeth Thysell estimates that the salmon can now migrate about one mil further up the river system and reach their important spawning grounds.
The salmon can now migrate about one mil further upstream and reach their important spawning grounds.
Important Habitat for the Sea Lamprey(
) The sea lamprey is often referred to as Sweden’s most endangered fish species. The species has a complex life cycle and initially lives as a larva in sediment banks before undergoing a transformation and later living as a blood-sucking parasite in the ocean. After several years, it returns to rivers to spawn.
The former migration barrier is gone. Salmon, sea lampreys, and other species can now migrate freely.
Photo: Nicka Hellenberg
Today, the species is found only in a few rivers in Halland and Västra Götaland. It is estimated that there are fewer than 50 adult individuals remaining from the previous year.
That is precisely why the restoration of the Okome Mill could be significant.
“With unobstructed migration routes and improved habitats, the species may be able to reach its upstream spawning grounds,” says Elisabeth Thysell, an expert on the sea lamprey and its biology.
Watch the news segment from Stockån in Halland. Biologist Elisabeth Thysell describes the value of the demolition of the Okome mill.
The work continues
Even though the major change has already been implemented, there is still work to be done. Stones, boulders, and dead wood will be returned to the river. At the same time, the idea is to let nature develop on its own as much as possible.
Elisabeth Thysell from the Halland County Administrative Board discusses the measures being taken in Stockån.
Photo: Nicka Hellenberg
To monitor developments, a fish camera has been installed in the river. Hopefully, the camera will provide a clearer picture of how salmon, sea lampreys, and other species use the restored waterway.
In addition to the natural values of the river, there is a cultural-historical aspect. The old dam environment has left its mark, and parts of the former dam embankment have been preserved so that visitors can see what the site looked like and how it functioned. In this way, the restoration is an initiative that both benefits nature and makes it possible to understand and preserve the site’s history.