A marine map used by Danish fishermen shows red markings that indicate areas off the island of Bornholm where fishing with trawler nets is discouraged. These zones contain a large amount of chemical weapons from World War II, dumped under the Soviet military administration between 1947 and 1948. The weapons lie at depths of 70 to 100 meters and include a range of chemical warfare agents. Estimates of the total amount of munitions vary, with some sources suggesting around 34,000 tons of weapons containing 12,000 tons of chemical agents, while others, including the Helsinki Commission (HELCOM), suggest higher figures—approximately 40,000 tons of munitions and 13,000 tons of agents. The exact numbers remain uncertain due to the secrecy surrounding the dumping operations at the time. The secrecy was further extended in 1997 when the defense ministries of the United Kingdom and the United States added an additional 20 years to the confidentiality period of these operations, delaying the release of detailed maps of the submerged areas. Mustard gas, one of the most common chemical warfare agents found in the area, does not dissolve in cold water and can form thick, sticky masses that remain hazardous for decades. Between 1994 and 2012, nearly 4 tons of mustard gas blocks were accidentally retrieved by fishing equipment off the coast of Bornholm. Most of these were discarded back into the sea by Danish authorities, while 196 tons of fish contaminated with mustard gas particles were removed from the market and destroyed during the same period. Danish authorities have recorded incidents of fishermen catching chemical munitions for many years, with HELCOM maintaining an annual register of such events. However, a decline in reported incidents may not necessarily mean the risk has decreased. It could be influenced by changes in fish populations, reduced fishing time, modern fishing technology, or gaps in national reporting. The Danish navy has systematically documented cases of accidentally caught chemical weapons for more than a decade, assessing the condition of the munitions and identifying high-risk areas. Research projects such as CHEMSEA (Chemical Munitions Search & Assessment), conducted between 2011 and 2013, have examined how chemical weapons degrade in the Baltic Sea, including in the Bornholm, Gotland, and Gdańsk basins. A scientific consensus suggests that the main dumping sites are well known, and the risk to coastal areas from chemical warfare agents is considered low. This is because hydrodynamic conditions in the area make it unlikely for toxins to spread widely. However, some munitions were thrown overboard during transport, sometimes in wooden crates that drifted beyond the intended dumping zones, which is why some marked fishing areas on maps extend beyond the original 1947 boundaries.