Norwegian Salmon Farms Dump Nutrient Waste Equal to Sewage of 30 Million People

Context Norway, home to the world’s largest farmed‑salmon industry, feeds fish in open‑net cages with protein‑rich pellets. Most of the feed’s nitrogen, phosphorus and carbon are excreted as faeces, urine or uneaten particles, and flow directly into fjords and coastal waters.

Key Facts In 2025 the sector released 75,000 metric tons of nitrogen, 13,000 metric tons of phosphorus and 360,000 metric tons of organic carbon. Those amounts equal the nitrogen load of sewage from 17.2 million people, the phosphorus load of 20 million, and the organic carbon load of 30 million. Data from Norway’s fisheries directorate and veterinary institute fed the calculation; researchers first summed total feed consumption, then applied known excretion rates to estimate how much of each nutrient remained in the water. Feed use rose 14.6 % over six years, mirroring industry expansion. Seasonal spikes pushed the highest nutrient loads into the water during summer, when cold‑water ecosystems absorb less. The Sunstone Institute’s report notes that fjords—semi‑enclosed basins—are especially prone to nutrient buildup, fostering algal blooms that consume oxygen when they die and decompose. Alexandra Pires Duro, a data scientist at Sunstone, highlighted that the waste output is three to five times what Norway’s 5.5 million residents would generate. “The faeces, the uneaten feed, the urine – everything goes into the water,” she said. Local officials have already acted, rejecting nine new farm applications in a fjord due to projected emission spikes. Environmental adviser Tom Pedersen called the report’s figures “conservative” and warned that decaying algae further deplete oxygen, a trend already observed in Sognefjord and Hardangerfjord. Industry representatives argue current production stays within natural carrying capacity, but acknowledge that further expansion could raise eutrophication risk in sensitive fjords.

What It Means The nutrient load rivals the raw sewage of a country the size of Australia, raising the likelihood of harmful algal blooms and oxygen‑depleted zones that threaten marine life and fisheries. Monitoring summer spikes and tightening site‑specific limits will be crucial as feed use continues to grow.

What to watch next Future reports from Norway’s Institute of Marine Research on the impact of planned production increases will indicate whether regulatory measures can keep fjord ecosystems from crossing critical thresholds.