Underwater war relics are increasingly being recognized as ecological time bombs, with the ocean floor hiding a silent and insidious threat. Researchers are diving to assess the scale of this hidden danger. There are approximately 2,000 such habitats at the bottom of the oceans, including abandoned naval vessels and even New York subway cars that have become artificial reefs for local marine life. These, at least, are free of toxic materials. In 1845, two ice-strengthened ships left England to attempt the fabled Northwest Passage, commanded by Sir John Franklin. None of the 129 men aboard returned. Those not deliberately sunk can threaten marine ecosystems. According to the International Maritime Organization, the ocean floor is littered with more than 3 million such wrecks. Ten years ago, a Danish diver named Gert Normann Andersen discovered one in the North Sea: a German submarine named UC-30. When it sank in April 1917 during World War I, it carried 18 mines and 6 torpedoes, equivalent to 3,000 to almost 5,000 kilograms of explosives. It is now part of the NorthSeaWrecks research project. The NorthSeaRegion project is helping mitigate the risks of the toxic legacy of war left on the sea bottom. The team has cataloged 10,127 wrecks in Danish waters, with about 15% linked to either of the two world wars. This includes millions of tons of munitions and chemical warfare agents, not to mention fuel oil or other hazardous cargo. Samples and videos taken by naval divers around the UC-30 reveal what could become an ecological catastrophe: explosive materials from the wreck diffusing into the surrounding marine environment. Researchers from Aarhus University (Denmark) mention in the Marine Pollution Bulletin that mines damaged by corrosion have been found, and traces of TNT have been detected in marine life, sediments, and water columns. However, the extent of the phenomenon and how far this pollution affects the marine environment remain unclear. Three centuries ago, a treasure worth nearly $400 million sank off the coast of Florida. A portion of this cargo was recovered in 2015 before authorities realized that part of it had been stolen during the excavation mission. Researchers have already reported alterations in enzymatic activity, metabolic disturbances, and a reduction in energy reserves necessary for essential biological processes such as reproduction in mussels they studied. The question is even more critical as the options available to governments for decontamination are limited. Sunken shipwrecks sometimes become popular diving sites and can attract biodiversity, especially when made of wood. However, they can also conceal dangers that scientists are only beginning to understand. Salvaging wrecks is not simple. Germany has already allocated significant funds to the salvage of certain wrecks and the recovery of World War II munitions in the Baltic Sea. It is worth noting that after the two world wars, governments disposed of millions of tons of surplus weapons by submerging them at sea or loading them onto old ships that were later scuttled. It was only later that it was realized that these wrecks degrade over time and release toxic substances into the marine environment. Attempting to destroy explosives in place does not help, as the shockwave tends to disperse contaminants in the water and worsen pollution rather than solve the problem. Sunken ships can serve as refuges for marine life, especially when made of wood. In the case of the wreck of the Portland, which sank in 1838, anemones, sea anemones, and a profusion of hydroids, bryozoans, and worm tubes have colonized the wooden stern. The only option left is the use of underwater robots. They could first help researchers closely monitor the condition of the wrecks. Then, they could map the precise location of hazardous munitions. Better still, they could, in the event of a confirmed pollution risk, retrieve these munitions to the surface where they could be destroyed safely. The Namib Desert, bordering the vast expanse of the Atlantic Ocean, is not only a vast arid region. A few years ago, archaeologists discovered a 500-year-old Portuguese shipwreck in Namibia from the 16th century containing a real treasure. Regardless of the option chosen, these efforts highlight the ecological legacy of war activities. They also draw attention to the 60 to 100 ships that sink each year worldwide due to collisions, unfavorable weather conditions, or aging hulls. These too release fuel and chemicals, as well as plastics that can persist in the ocean for centuries.