Oxygen pumps revive dead zones in Oslofjord

A once-dead section of Oslofjord is showing signs of recovery after two years of oxygenation efforts, with returning marine life and improved water quality, reports Dagbladet.

In spring 2024, the deep-water area between the islands of Ormøya, Ulvøya, Malmøya, and Paddeøya—known as Paddehavet—was completely devoid of oxygen below 12–13 meters, with stagnant, murky water. Now, after continuous pumping of oxygen-rich surface water to the seabed, conditions have improved significantly.

Oxygen levels have extended two meters deeper, reaching 13.5 meters, while water quality scores have more than doubled—shifting from “poor” to “moderate to good.” Bottom water renewal in 2025 replaced old, oxygen-depleted water with fresher supplies.

“We hope the fjord floor can now begin repairing itself,” said Arild Hartmann, technical director at Hafslund Kraft, which operates the pumping station. However, he noted that seabed areas remain lifeless, requiring further measures to restore ecosystems.

The project, now entering its third season, uses three electric pumps powered by solar panels and land-based electricity to circulate surface water. Live camera footage shows returning herring schools and tunicate growth—signs of ecological progress.

“What’s happening here is like an aquarium without an air pump: it quickly becomes overgrown,” said Finn Bjørn Ruyter, CEO of Hafslund. “Excess nutrients from sewage and agriculture, combined with oxygen depletion, choked this area. Two years of pumping are changing that.”

Hafslund plans to scale up similar efforts, emphasizing the fjord’s hidden crisis: “Oslofjord looks idyllic on the surface, but vast dead zones lie beneath,” Ruyter said. The company will host Norway’s first cross-disciplinary nature conference in June to prioritize environmental action.

Oslofjord, once Norway’s most biodiverse fjord, faces threats from nutrient runoff, coastal development, overfishing, pollutants, and climate change. Species like cod, mussels, kelp, and eelgrass have declined sharply in recent decades.