Nearly 40% of fish died in first hit from 2025 algae crisis.
A research paper published in the Journal of Fish Diseases has documented 39.5% acute mortality at the first salmon farm struck by the 2025 algae bloom in northern Norway.
The paper, titled “First Strike: Description of the Events at the First Salmon Farm Affected by the 2025 Algal Bloom in Northern Norway,” was authored by Julie Seem as part of her PhD research with Nordlaks ASA. It covers the outbreak at Nordlaks’ Fornes site in Øksfjorden, where more than one million Atlantic salmon with an average weight above three kilograms were held at the time.
What happened at Fornes
The first signs were reduced appetite and turbid water, followed by behavioural changes and rapid fish death. Water samples confirmed dominance of Phaeocystis pouchetii and Chrysochromulina leadbeateri. Post-mortem examination and histopathological findings in gills and liver confirmed algae as the cause of death.
Nordlaks activated its emergency plan immediately and halted feeding. All fish at the site were subsequently emergency harvested. CEO Eirik Welde previously described the mortality as arriving “out of nowhere” and called the situation “terrible.”
The company estimated total losses from the broader 2025 bloom — which also affected Ellingsen Seafood and Kleiva Fiskefarm — at a minimum of NOK 300 million (EUR 30 million).
Gaps in monitoring
The paper concludes that the Fornes event “underscores the urgent need for monitoring and early warning systems for harmful algal blooms,” as well as improved emergency response protocols.
Seem said published data on algae events in fish farming is sparse, making the study a rare empirical reference for the industry.
The Norwegian Institute of Marine Research has already issued algae warnings for farms in Agder and Rogaland, suggesting the problem extends beyond northern Norway.