Norwegian fish farms are filling fjords and coastal waters with nutrient pollution equivalent to the raw sewage of tens of millions of people each year, a report has found. The Sunstone Institute analysis reveals that aquaculture released 75,000 tonnes of nitrogen, 13,000 tonnes of phosphorus and 360,000 tonnes of organic carbon in 2025.
The nutrient levels are comparable to the untreated sewage of 17.2 million people for nitrogen, 20 million for phosphorus, and 30 million for organic carbon. ‘Norway is a small country of just 5.5 million people, and the output of aquaculture pollution in terms of these three nutrients is three to five times larger than the population,’ said Alexandra Pires Duro, data scientist at Sunstone and author of the report. ‘The faeces, the uneaten feed, the urine – everything goes into the water.’
Fish in open-net cages are fed nutrient-rich pellets, with waste excreted directly into the water. Feed consumption rose by 14.6% over six years, in line with industry expansion. Seasonal variation worsens the problem, with nutrient load highest in summer when ecosystems are least able to absorb it.
The fish sludge can trigger destructive algal blooms that deplete oxygen, particularly in semi-enclosed fjords. In Sognefjord, increased nutrient inflows were blamed for about two-thirds of oxygen depletion last year, with warmer water accounting for the rest. Oxygen levels have also declined in Hardangerfjord, leading officials to reject nine fish farm applications in March due to emissions concerns.
Krister Hoaas of the Norwegian Seafood Federation defended the industry, stating that emissions reflect food production and self-sufficiency, and that current operations are within nature’s carrying capacity according to the Institute of Marine Research. ‘It is important to distinguish between current operations and questions about future growth,’ he added.
