Norwegian fish farms polluting fjords

Norwegian fish farms are filling fjords and other coastal waters with nutrient pollution equivalent to the raw sewage of tens of millions of people each year, a report has found.

Norway is the largest farmed salmon producer in the world, and nutrients in fish feed are excreted directly into coastal waters.

Analysis from the Sunstone Institute found that Norwegian aquaculture released 75 000 tonnes of nitrogen, 13 000 tonnes of phosphorus and 360 000 tonnes of organic carbon in 2025.

The nutrients are equivalent to those contained in the untreated sewage of 17.2 million people for nitrogen, 20 million people for phosphorus and 30 million people for organic carbon, raising fears of destructive algal blooms.

“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,” says Sunstone data scientist Alexandra Duro.

Fish in farms are fed pellets of nutrient-rich feed in open-net cages as they are grown for human consumption.

The analysts calculated the mass of nutrient inputs that remained in the water using data from the national fisheries directorate and veterinary institute.

Fish sludge from nutrients can fertilise phytoplankton and lead to destructive algal blooms that deplete oxygen levels.

Fjords are particularly vulnerable to such effects because they are semi-enclosed bodies of water, allowing for greater nutrient accumulation.

In Sognefjord, the country’s longest fjord, increased nutrient inflows were held responsible for about two-thirds of the oxygen depletion, a study found last year, while warmer water was blamed for the other third.

In March, officials rejected nine applications for fish farms in the fjord on account of the increased emissions they would cause.

Environmental adviser Tom Pedersen says the figures in the analysis were unsurprising and even “on the conservative side”.

“The major concern we experienced in the last few years is that all these algae and plankton and whatever die and they sink down to the bottom of the floor and they decompose – and that process uses oxygen,” he says.

“The end result is that the oxygen level in the fjord is going down, and has gone down.”

The Norwegian fisheries ministry referred a request for comment to the fisheries directorate, which declined to comment.

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