Late last year, scientists in Germany published some remarkable findings on a second world war munitions dump in the Baltic Sea. Some may dismiss the dump as hazardous waste, but to marine biologists it was something far more exciting: a thriving ecosystem.
Over the decades, the dump has become home to mussels, crustaceans, fish and marine plant life, creating a full community under the sea. It’s a perfect example of an accidental reef, highlighting nature’s ability to reclaim even dangerous human detritus.
Around the UK coast, there are thousands of famous wrecks. I have had the pleasure of diving on many of them, witnessing first hand how sea creatures turn rusting hulls into habitat. Further afield, deliberate artificial reef projects, from Australia to the Caribbean, are evidence that where structures sink, life follows.
But let’s not romanticise our wrecks. While these structures offer a foothold for life, they can also leak toxic compounds into the oceans.
Scuppered ships
Not all reefs are born from disaster. Around the world, governments, scientists and conservation groups have deliberately sunk ships, concrete structures and even old underground train carriages to create new marine habitats. These artificial reefs are designed to mimic the ecological functions of natural reefs, boosting biodiversity and providing refuges for overfished species. They also draw scuba divers and recreational fishers, providing economic incentives for people who live nearby.
In the US, the decommissioned aircraft carrier the USS Oriskany was famously sunk to create a tourist attraction off the Florida coast: the “Great Carrier Reef”. In November 2026, an even bigger ship will be sunk nearby: the SS United States, an ocean liner larger than the Titanic.
PTS Aerial Services / shutterstock
In Japan, concrete blocks have been used extensively to stabilise coastlines and provide habitat for fish. In Australia, the “rigs-to-reefs” initiative means old oil rigs – too costly to remove – are being left in place to create new ecosystems.
But there’s a fine line between “marine habitat creation” and simply “dumping unwanted stuff”. Poorly planned projects have often done more harm than good.
Perhaps the most infamous case is the Osborne Reef off Florida. In the 1970s, millions of used vehicle tyres were sunk to create a massive reef. But the steel clips holding them soon corroded, and many tyres broke loose and started scouring the seafloor and battering a nearby natural coral reef during storms.
The expensive lesson is that artificial reefs can at best supplement conservation, but they are not a substitute for protecting natural habitats.
A less visible legacy
Shipwrecks and artificial reefs also bring with them a less visible legacy of metal pollution.
The vast majority of wrecks are made of steel, iron, copper and various other alloys that slowly corrode in seawater. This releases dissolved metals into the surrounding environment, and while iron and steel often rust away harmlessly, other metals can be more problematic.
Copper, zinc, lead, tin and aluminium can leach from hull coatings, machinery, or electrical components. These trace metals and toxic chemicals don’t just wash away. Instead, they accumulate in surrounding sediments and, more worryingly, in the tissues of marine organisms. This is particularly concerning for filter feeders such as mussels and oysters, which can concentrate pollutants and pass them up the food chain to predators – and potentially humans.
In high enough concentrations, these substances become toxic, affecting growth, reproduction and survival. For instance, for many years ship’s hulls were coated with the chemical tributyltin (TBT) to prevent barnacle growth which slows vessels down. However, TBT also caused serious environmental damage: some female dogwhelks developed male sexual organs, for instance, disrupting reproduction cycles in these key coastal molluscs.
The issue is magnified for wrecks that still contain fuel or munitions. Corroding shells and tanks not only release components of explosives but also heavy metals such as mercury, arsenic, lead, cadmium, chromium and TNT degradation products.
The Baltic Sea munitions, for example, are slowly leaking toxicants into an already fragile semi-enclosed sea. If fish are still there, how bad can the contamination really be? The problem is that presence does not equal a safe zone. Many toxic metals and explosive residues cause sub-lethal effects that do not immediately drive fish away or kill them outright. Instead, these substances accumulate through the food web. Fish may continue to hang out in contaminated areas while suffering impaired reproduction, altered behaviour, suppressed immune systems, or developmental defects. These effects are ultimately largely invisible without detailed study.
In a semi-enclosed system like the Baltic Sea, limited water exchange exacerbates the problem: contaminants persist longer, sediments act as long-term reservoirs, and chronic exposure becomes unavoidable. What looks like ecological resilience can therefore mask a delayed population collapse, and increased risk to predators, including humans, who potentially consume the fish.
We know that organisms can tolerate pollution in the short term. The question is whether ecosystems can remain functional and safe under decades of continuous, low-level toxic exposure.
Supplement not substitute
The urgent need to create artificial habitats is heightened by the crisis facing natural coral reefs from climate change, ocean acidification, overfishing and pollution. Rising sea temperatures are already triggering mass coral bleaching events.
In this context, wrecks and artificial reefs also serve as accidental laboratories. They show how quickly life will colonise and exploit a new habitat, providing lessons for restoration work elsewhere. But the answer to the reef crisis isn’t simply “sink more ships”.
Artificial reefs should never be seen as a licence to pollute or a shortcut for true conservation. They must complement, not replace, efforts to protect and restore natural habitats. We can’t “offset” destroying an ancient coral reef by sinking an old ship. Conservationists rightly stress the focus must remain on marine protected areas, reducing ocean acidification, tackling overfishing and pollution.
The Baltic Sea munitions “reef” is an accident of history rather than a model for the future. Yes, marine life has flourished there, but it swims in a sea filled with heavy metals and toxins.
Nicholas Ray does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.