Oxygen levels in Norway fjords down 15%, caused by nutrient overload and ocean warming

Oxygen levels in the deep waters of several fjords on Norway's west coast have fallen by around 15 percent over the past 30 years, according to a new government report. The main causes are climate change and nutrient waste from fish farming, agriculture, wastewater, and industry. One-third of the decline is attributed to climate-related warming, while two-thirds stems from nutrient and particle loading.

Fjords on the west coast of Norway are vulnerable because they are shallow at the mouth but deep inside, so the inflow of oxygen-rich seawater from the ocean is limited. This makes them more susceptible to stress from warming and nutrient input.

The report notes that since 1990, nitrogen input to Sognefjorden fjord has increased by 50 percent, and phosphorus by 240 percent. Aquaculture is cited as the largest contributor of both.

While there is currently no acute threat to marine life, the director of the Norwegian Environment Agency warned that continued deoxygenation could increasingly disrupt the fjord. "This is not yet critical, but if the trend continues, conditions for marine life will become increasingly difficult," she said.

• Read the full article in Salmon Business, 14 April 2025