Vejle Fjord oxygen depletion remains a serious problem, but new measurements and long-term monitoring suggest that Denmark’s largest marine restoration project is producing results in parts of the fjord. Greenpeace Denmark and the Danish Anglers Association (Danmarks Sportsfiskerforbund) returned to Vejle Fjord on Wednesday, 12 August, more than two years after symbolically declaring it “dead”, finding oxygen-poor conditions at two locations while scientists reported improving biodiversity in areas where eelgrass, mussel beds and stone reefs have been restored.
The environmental organisations brought oxygen-measuring equipment and red flags marked with a white fish, intended as a warning sign for areas where marine conditions were considered unsafe for aquatic life. According to DR, Greenpeace eventually placed two flags after measurements showed moderate oxygen depletion close to the threshold for severe depletion and a largely barren seabed.
The flags were removed after the approximately five-hour action and will now be used as Greenpeace takes the campaign to other Danish fjords.
Vejle Fjord oxygen depletion varies considerably by location
The measurements, however, provide only part of the picture. Vejle Fjord is continuously monitored by eight measuring stations that record environmental conditions every ten minutes throughout the year.
Mogens Flindt, professor of biology at the University of Southern Denmark (Syddansk Universitet), told DR that frequent oxygen depletion occurs in the inner fjord between the Vejle Fjord Bridge and the city of Vejle. Further east, particularly at depths of up to four or five metres, oxygen depletion is recorded much less frequently.
At greater depths, including areas around ten metres deep, oxygen-poor conditions remain a problem even in the outer fjord.
This geographical difference is significant because the shallower parts of the fjord are also where much of the restoration work is taking place.
“As soon as we move away from the innermost part of the fjord, our nature restoration is working very well,” Flindt told DR. “We have planted eelgrass over a longer period, and we can follow how biodiversity increases over time.”
The University of Southern Denmark, which participates in the project and analyses monitoring data, describes Vejle Fjord as an ecosystem still in poor condition, affected by excessive algae, declining eelgrass, a lack of fish and recurrent oxygen depletion. Its research also indicates that the ecosystem has struggled to recover without active intervention.
Eelgrass and stone reefs are bringing back marine life
The restoration programme Healthy Vejle Fjord (Sund Vejle Fjord) has become the largest marine nature restoration project of its kind in Denmark, according to Flindt.
The programme combines four main measures: replanting eelgrass, creating mussel beds, establishing stone reefs and reducing crab populations. The aim is not simply to improve water chemistry but to recreate habitats capable of supporting a more diverse marine ecosystem. Vejle Municipality has allocated more than DKK 25 million (about €3.3 million) to the five-year restoration effort.
The results also illustrate the limits of local restoration. Eelgrass cannot simply be replanted throughout the fjord: in deeper water, insufficient light prevents it from growing. Restoring habitats therefore cannot by itself eliminate the conditions that cause oxygen depletion.
Research led by Flindt has stressed that re-establishing eelgrass beds can help recover healthier ecosystems and prevent fast-growing algae from dominating coastal waters, but restoration projects need suitable environmental conditions to succeed.
Greenpeace says “pockets of life” are not enough
Greenpeace acknowledged the improvements where restoration has taken place but argued that healthy areas within the fjord should not obscure its wider ecological problems.
“It is really great if there are some pockets of life in Vejle Fjord, but we should also be able to demand that there are not just pockets of life in the fjord, but that life is actually possible throughout the fjord,” Emil Bejer-Pedersen, campaign manager at Greenpeace, told DR.
Greenpeace argues that the underlying problem remains excessive nutrient pollution, particularly nitrogen runoff from agriculture, which stimulates algal growth and contributes to oxygen depletion when organic material decomposes. The organisation has made reductions in agricultural nitrogen emissions a central part of its campaign over Denmark’s marine environment.
The group and the Danish Anglers Association drew national attention to Vejle Fjord in April 2024, when they organised a symbolic funeral for the fjord following years of declining marine life and severe oxygen depletion. A gravestone used in the demonstration read: “Here rests Vejle Fjord. May you rise again.”
Vejle Fjord shows both the potential and limits of restoration
Flindt cautioned against presenting Vejle Fjord as uniquely damaged. He told DR that conditions are considerably more degraded in several other Danish waters, including Haderslev Fjord, Flensburg Fjord and Limfjorden.
The contrast within Vejle Fjord is nevertheless important. Greenpeace’s measurements show that oxygen depletion and barren seabeds persist in parts of the fjord, while the monitoring data indicate that carefully targeted restoration is helping marine life return elsewhere.
The municipality is now also exploring a broader long-term nature project covering Vejle Ådal and Vejle Fjord, linking marine restoration with changes in surrounding landscapes and land use. The initiative is being developed as part of Denmark’s Green Tripartite framework and would rely on voluntary agreements with landowners.
Vejle Fjord therefore offers a relatively clear example of the challenge facing many Danish coastal waters. Habitat restoration can rebuild ecosystems where conditions permit, but reducing the pressures that cause oxygen depletion remains necessary if those improvements are to extend beyond isolated areas.
