Norway’s Driva river to undergo chlorination treatment for salmon parasite elimination

Norway’s national salmon river, Driva, is set to undergo a chlorination treatment to eliminate the salmon parasite Gyrodactylus salaris, despite the construction of the country’s largest fish barrier in 2017 aimed at preventing this issue. Environmental DNA testing has confirmed the presence of salmon in the river, which is considered unusual. The treatment will span a total of 100 kilometers, rather than the initial 20 kilometers planned.

Chlorination is deemed safe for the salmon and trout populations, targeting only the parasite. There is considerable optimism regarding the success of this treatment.

The chlorination solution will be released into Driva, flowing through the regions of Innlandet, Trøndelag, and Møre og Romsdal. Gyrodactylus salaris has been a concern in several Norwegian salmon rivers since 1975. Originally, it was believed that the fish barrier would prevent the need for a full river treatment, as it was intended to block spawning fish and allow them to eventually exit to sea, thus allowing the parasite to die out.

However, recent environmental DNA analysis has shown that salmon still resides in the river, prompting the Norwegian Environment Agency to adjust their plans. Chlorination will now take place above the barrier as well. The dosage will be adjusted to levels comparable to the drinking water in Oslo, ensuring it effectively targets the parasite without harming other fish.

The presence of salmon at high altitudes in Driva is rare, as these fish typically thrive at elevations of up to 600 meters, resulting in slower growth rates and delayed migration to the sea. While officials cannot guarantee the river will be free of the parasite afterward, they are hopeful for a successful outcome.