Denmark dumped 18.4 million cubic metres of dredged seabed sediment at sea between 2015 and 2023, according to a new analysis by Tænketanken Hav (Think tank Ocean).
That equals just over 2 million m³ a year, or the load of about 87,000 lorries each year. The practice has clear local harm to marine life and spreads hazardous substances, the report says.
Scale and sources of dumping
Most dumping permits came from ports. Around 60% of permits issued in 2020–2023 were linked to ports and their contractors, mainly for dredging shipping lanes and harbour works.
The rest came from large marine construction projects, such as bridges and tunnels. In total, 64 active dumping sites were used in Danish waters in that period.
Risks to marine life
International research reviewed in the analysis shows that dumping harms seabed animals at disposal sites and spreads nutrients and hazardous substances.
These include heavy metals and oil-related compounds that can increase mortality and affect reproduction in bottom-living species. Fine sediment can also reduce light in the water, harming eelgrass and seaweed, and can damage fish spawning grounds.
Call for alternatives
The report says impacts can already be reduced with existing tools, such as better planning, reuse of clean sediment, and less harmful placement methods.
Over time, it urges Denmark to avoid dumping as far as possible and replace it with prevention and more circular uses of sediment, treating it as a resource rather than waste. Ports are highlighted as key drivers of change.