A German submarine that sank off Denmark in 1917 still holds over 4,400 pounds of TNT; scientists find explosive leaking into North Sea

A German submarine that sank off Denmark's Rømø island in 1917 is leaking TNT into the North Sea, according to a finding announced by Aarhus University on August 27, 2026. Researchers found the chemical in seawater, sediment and even animals at the site. Blue mussels left for at least 11 weeks at the hull of the submarine that lies about 6 miles off the Danish coast, had absorbed it too.

A 2024 report for Denmark’s Environmental Protection Agency estimates the wreck of UC-30 still holds about 2,000 kg of the explosive.Katrine Juul Andresen, a geoscience professor at Aarhus University, examined UC-30 through the European NorthSeaWrecks project. Civilian diving is banned at the wreck, and naval charts mark a restricted zone 328 feet (100 meters) around it. Danish navy divers therefore collected the samples after she briefed them.Along with water and sediment, the divers brought up starfish and mussels living on the submarine as samples.

Romina Marietta Schuster of Germany’s Alfred Wegener Institute led the mussel study, with Andresen among the coauthors.