Western Norway hit by strongest marine heatwave in decades.
Western Norway experienced its most powerful marine heatwave since at least 1990 this summer, according to the Institute of Marine Research.
The heatwave lasted 29 days from 9 July and reached the “strong” category, the second-highest level. At the Bud monitoring station in Hustadvika, sea temperatures peaked at 18°C compared with a normal range of 12–14°C. Satellite data indicated a maximum of 20.4°C north of Bud.
Researchers warned that kelp forests, seagrass, shellfish, and farmed fish are particularly vulnerable to such events. Warmer seas also accelerate the life cycle of sea lice, making them reproduce and attach to salmon more easily.
August 2025 saw the highest recorded levels of adult female lice on farmed fish in Northwest Norway and Trøndelag, with several sites struggling to remain below regulatory thresholds.
