The following is a news article about Chemical Weapons off the New Jersey, USA coast. Seems the Army just dumped them 20 miles off the coast after the war ended.
"Chemical Weapons Dumped Off NJ's Coast
The US Army now admits that it secretly dumped 64 million pounds of nerve and mustard agents into the sea, along with 400,000 chemical-filled bombs, land mines, and rockets, and more than 500 tons of radioactive waste, either tossed overboard or packed into the holds of scuttled vessels. These weapons virtually ring the country's coast. The Army has examined only a few of its 26 dump zones and none in the past 30 years, and records are sketchy, missing, or were destroyed. Army cannot say exactly where all the weapons were dumped from World War II to 1970 and, furthermore, the Army has not reviewed World War I-era records, when ocean dumping of chemical weapons was common.
In the summer of 2004, a clam-dredging operation off New Jersey pulled up an old artillery shell. The long-submerged World War I-era explosive was filled with a black tar-like substance. Three bomb disposal technicians from Dover Air Force Base, DE, who were brought in to dismantle it, and were injured from exposure to mustard gas. The shell was filled with mustard gas in solid form and was pulled up with clams in relatively shallow water only 20 miles off Atlantic City. In fact, 1985 charts from the National Oceanic Atmospheric Administration (NOAA) identify numerous areas where explosives and weapons were disposed in the NY/NJ Bight.
When mustard gas is exposed to seawater, it forms a concentrated gel that lasts for at least five years, killing or contaminating sea life. When released in the ocean, nerve agent lasts up to six weeks, killing every organism it touches before breaking down into its non-lethal chemical components.
The Army's secret ocean-dumping program spanned decades, from 1944 to 1970. The dumped weapons were deemed to be unneeded surplus. US Congress banned the practice in 1972. Three years later, the United States signed an international treaty prohibiting ocean disposal of chemical weapons."
Have also read articles that there is a huge amount of Chemical Weapons from the same war off the Belgian Coast.