Rusting World War II munitions are poisoning the Baltic Sea as Germany begins cleanup

Approximately 1.6 million tons of ammunition from the two world wars lie on the floors of the North Sea and Baltic Sea, and German authorities say the corroding ordnance is increasingly contaminating the Baltic — prompting a government-backed pilot to recover and safely dispose of munitions.

The current four-week operation, staged from the self-propelled crane barge Baltic Lift about 6 kilometers off Boltenhagen on Germany’s Baltic coast, is targeting a field estimated to contain roughly 900 tons of old shells and grenades. Divers working in rotating 12-hour shifts recover items, which are stored underwater in baskets until a special ship takes them ashore for disposal at facilities equipped to handle legacy explosives.

Divers say the work is hazardous. Dirk Schoenen, a volunteer diver with the Baltic Taucher team, described slowly lifting shells and grenade fragments from the seabed and placing them into baskets while a team of engineers and seamen monitored his head-mounted camera. Salz and oxygen have eaten through many casings, exposing explosive material and making some detonators increasingly sensitive, though explosions remain a rare occurrence, officials said.

The urgency stems as much from chemical contamination as from explosive risk. Studies cited by the German environment ministry and the GEOMAR Helmholtz Centre for Ocean Research Kiel have detected breakdown products of TNT and related explosives in water near munition sites. Those substances are considered hazardous and have been found to accumulate in marine organisms such as mussels and fish. While measured concentrations have generally remained below regulatory safety thresholds, GEOMAR said some readings "approached critical levels" and warned of long-term risks if munitions clearance does not proceed.

The Baltic’s restricted connection to the North Sea and Atlantic means water exchange is slow; contaminated water can remain in the basin for decades, increasing the potential for accumulation in the ecosystem, the environment ministry said. The problem is not unique to Germany: officials and experts note similar risks in other seas, including the Black Sea, where munitions from more recent conflicts are raising fresh concerns.

Most of the ordnance was deliberately dumped at sea after World War II. Allied authorities ordered the destruction of German stockpiles and, in 1946, trains carried armaments to coastal disposal points. Fishermen and military teams transported and sank material in designated areas, though some consignments were dumped elsewhere. Strong currents, particularly in the North Sea, have since dispersed many items across broad swaths of seafloor.

The German government has allocated about 100 million euros to study and address the problem. The current small-scale recovery is one of several government-sponsored efforts, including projects last year that used underwater robots to map and screen the seabed for munitions. Engineers leading the program say findings from these operations will inform the design of longer-term solutions, such as automated remote systems to recover ordnance and industrial facilities that could neutralize explosives offshore without exposing divers to undue risk.

Volker Hesse, a marine engineer coordinating the cleanup program, said the work has international relevance. “This is definitely a global problem — one only has to think of the crises in Vietnam or Cambodia, but also here locally in the neighboring countries, the Baltic Sea, Denmark, Poland,” he said, noting that lessons learned will be shared with other nations facing legacy contamination.

On deck, recovered shells and fragments are not handled casually. Divers wear multiple layers of gloves and follow strict protocols to avoid skin contact or accidental impact. Because the material is too unstable to be dismantled on the platform, it is kept under water in baskets and transferred to a specialized vessel for transport to shore-based disposal sites.

Researchers and authorities stress that while most of the detected contamination remains below immediate health and safety thresholds, the potential for chronic harm to marine ecosystems and the widening geographic scope of underwater munitions deposits make clearance a pressing environmental and public-safety priority. The pilot off Boltenhagen is intended to test practical approaches for recovery and to help planners develop methods for wider-scale remediation of underwater munitions in the Baltic and beyond.