The summer of lurv
The pollution from salmon farming peaks exactly when it is most harmful to underwater forests.
Lou Luddington (text) & Aleksander Nordahl (text and visuals)
The air temperature is below zero as Aleksander Nordahl and a freediving companion slip into wetsuits and gather their dive gear. They have travelled to a fjord in the far southwest of Norway to document the seabed underwater.
It is February, 2025. Sliding into the water they feel its icy sting as it reaches their exposed cheeks. Kicking with long fins, they surge through the frozen surface, cracking a seapath to deeper water and the wastewater pipes from a salmon hatchery, 100 metres offshore.
A few metres below the pipes, the seabed is barren and black as a lava landscape.
Humps of decomposing lurv are everywhere. These hair-like algae now dominate Norway’s underwater habitats. They bloom in summer, then die off in winter, becoming food for bacteria that deplete the seabed of oxygen.
The scene is littered with their decaying, lifeless tangles.
Swimming towards the rocks, Nordahl notices splashes of crimson, orange and rose poking through the shrinking layer of lurv.
Dahlia sea anemones dotted here and there, bloom like flowers in the sunshine, and look out of place in these gloomy surroundings.
They belong here and are profiting from the buffet of organic waste spilling from the pipes. Usually found below the kelp forest canopy, only a few dishevelled kelp plants remain.
The divers leave the water feeling a sense of loss at having witnessed an ecosystem in decline.
At the beginning of August 2025, Nordahl returns. The water is cloudy with waste from the hatchery pipes and lurv grows in thick carpets, shrouding the seabed. The forlorn kelps and opportunistic sea anemones are still there but swamped by the expanding lurv.
Sunstone Institute research shows that nutrient pollution from salmon farms peaks in summer. This favours lurv and disfavours kelp. Whereas lurv thrives on summer’s profusion of fish farm nutrients, warmth and sunlight, Norway’s underwater forests struggle and shrink. Based upon a perilous mismatch in biology between salmon, lurv and kelp, this produces a slow but relentless battle that is being won by lurv.
Alsaker fjordbruk, the operating company of the hatchery shown above, has been given the chance to comment on the video documentation. The firm has not responded in time for publication.
Hidden in the seasons
Regulators judge a salmon farm's environmental footprint using annual averages, treating fish waste as a steady, year-round drip. But because salmon are cold-blooded, their feed intake and waste excretion rise and fall with seasonal water temperatures. Salmon growth is optimal at 10–14 °C and coincides with summer sea temperatures in Norwegian waters. This is when growth is fastest and they are fed more than double the winter amount. In 2025, feed consumption rose from 140,617 tonnes in March to a peak of 244,739 tonnes in September, according to the Norwegian Directorate of Fisheries. This extra feeding and raised metabolism create a spike in waste nutrient levels in summer waters—exactly when lurv thrives.
According to Sunstone’s calculations, an 80% increase has been recorded for all nutrients between March and September. That’s just five months. When compared to how much human sewage this nutrient pollution represents, nitrogen from Norway’s salmon farms ballooned from equivalent to the sewage from 12.45 million people in March to a staggering 22.40 million in September in 2025. For phosphorus, 14.44 million became 25.97 million and for organic carbon, 21.40 million rose to 38.49 million.
By relying on national annual averages, regulators miss the messy reality of summer’s overload, especially in densely farmed areas. Instead of an annual average equivalent to three times the population of Norway, the summer level shoots up to more than four times. Hidden among the averages authorities use to monitor salmon farm waste, the summer spikes get overlooked. This results in the statistical dilution of risk in a single year. At the same time, the industry continues to grow. In 2025, salmon farming in Norway boasted the highest annual salmon production since 1980.
"Annual averages can obscure short‑term peaks that matter locally, especially in areas with poor water exchange during periods of high biological activity", admits State Secretary to the Minister of Climate and Environment, Kristoffer André Hansen, in an e-mail to Sunstone.
When asked whether they will mandate seasonal, site-specific monitoring, he says that more targeted monitoring may be required, "where evidence shows a need, particularly in vulnerable fjords". At the same time, he upholds that lurv is not a widespread, national problem.
The biological mismatch
The overlooked seasonal ebb and flow of salmon farm waste amplifies the lurv catastrophe unfolding along Norway’s coasts. To understand how, requires a dive into the natural biological cycles that have helped shape these underwater ecosystems over thousands of years.
In a healthy ecosystem, kelp shows distinct seasonal patterns of growth in tune with natural environmental fluctuations. In summer, when daylight is plentiful, the focus is on making and storing sugars through photosynthesis. At this time, growth is slow. In winter and early spring, growth peaks, as storms churn the fjords, bringing deep-water nutrients up to the surface. Tapping into this rough weather bounty and using carbohydrates stored during the summer, native kelps have evolved to maximise growth in winter and spring. By the time summer arrives and the waters calm, natural nutrient levels in the sea plummet, and the kelp switches to accumulating sugar reserves for winter again. This strategy allows them to avoid natural limitations on nutrients and light through the seasons.
But the salmon farm industry upends this cycle. Just as coastal waters reach their natural, nutrient-scarce summer phase, waste from open-pen farms peaks.
The sudden influx of fertiliser cannot be absorbed by the native kelps. Instead, it feeds the lurv; fueled by a spike in nitrogen equivalent to 22.4 million people excreting directly into the sea, these fast-growing, opportunists thrive.
With unlimited nourishment and profuse sunlight, their shaggy carpets spread across the seabed, overgrowing and shading out the seaweed gardens and kelp forests below. In a study of sugar kelp in southern Norway, scientists found that shading by lurv significantly slows kelp growth and increases death rate. Overgrowth also smothers the seabed where young kelp might otherwise settle and grow.
For kelp, lurv is bad news.
The new normal
Summer provides ideal conditions for lurv to bloom and take over. Plentiful sunlight for photosynthesis, warmer temperatures and high nutrient load in the water from human sources. These nutrients come from industry, agricultural run-off, municipal wastewater and sewage, and run-off from built up areas, but in Norway, aquaculture is the single largest source.
When asked about the relationship between lurv and salmon farm waste, senior scientist and kelp expert Hartvig Christie says, “It is highly likely that lurv growth in summer is enhanced by salmon farm waste in areas with high densities of fish farms”. He admits that it is not scientifically documented. It is very difficult to design studies and document changes in marine ecosystems because the challenges are so complex, he says. “Also there are no control areas left.”
With the whole coast of Norway now affected by lurv, there are few places to compare it to. Throughout the world’s ocean, the loss of natural baselines has led to Shifting Baseline Syndrome (SBS), which describes the gradual shifting of the accepted condition of natural environments. Each new generation of humans accepts the depleted state they grew up with as normal.
The effects of climate change are already apparent in Norwegian coastal and fjord areas, leading to, amongst others, increased water temperatures and reduced oxygen levels in the water. These changes are leading to less robust ecosystems and reduced tolerance to environmental impacts from salmon farming. Predictions show these changes intensifying into the future.
Some studies suggest the ocean is simply getting too warm for native, cold-adapted kelp to survive. This may also be true in some areas, but it is amplified by the added stress of seasonal nutrient loading and lurv overgrowth compromising kelp growth, reproduction, recovery and adaptation to a changing ocean.
The situation is made worse by kelps sensitivity to warming sea, “Kelp are stressed by high temperatures, ” Christie explains. As baseline ocean temperatures rise, Norway's kelp becomes more vulnerable to the effects of nutrient pollution. Kelp forests are being lost to the creep of lurv all along the coast, yet they are vital for ocean health.
As keystone species, they provide food, shelter and nursery areas for a rich biodiversity of life. They also protect our coastline, sequester carbon and improve water quality.
Beyond average
Using annual averages to evaluate nutrient pollution from salmon farms underestimates the ecological pressure on Norwegian coastal ecosystems. For kelp forests, the timing of pollution is critical.
A concentrated pulse of nutrients in summer amplifies pressure on these underwater forests just when they are gathering stores for winter growth, and are most vulnerable to smothering by lurv. Understanding the nuances of both kelp and salmon lifecycles highlights the importance of assessing nutrient pollution from a seasonal perspective. For authorities responsible for regulation, fluctuations revealed by monthly data provide a clearer picture of ecological risk than yearly averages.
“The government’s goal of further growth in aquaculture cannot come at the expense of fjord and coastal ecosystems”, says State Secretary to the Minister of Climate and Environment. “Climate change may increase vulnerability over time, and if cumulative pressure becomes too high, stricter requirements must be imposed”.
According to Christie, in some areas, Norway’s underwater forests have already reached a tipping point. They have been lost to a summer of lurv, where the story playing out is one of tragedy, not romance, for these ancient Arctic jungles.
But it’s not too late. As with so many challenges facing the ocean today, we already have the data, knowledge and technology to turn things around. The next chapter will be written by regulators and decision makers willing to re-evaluate, and respond with the urgency required.
Additional credits:
Data analysis/story design: Carter Ronald Brown
Story Editor: Ingerid Salvesen
Copy editor: JohnJo Devlin
Managing editor/creative director: Aleksander Nordahl
Publisher: Jan Grønbech
Special thanks to external experts Tom N. Pedersen (Senior advisor on aquaculture) and Hartvig C. Christie (Marine biologist and senior scientist)