A Canadian diver looking for sea cucumbers off the coast of western Canada found something much larger than he had hoped: a possible nuclear bomb.

While diving recently off Pitt Island near Haida Gwaii, Sean Smyrichinsky may have stumbled on the device jettisoned by a B-36B bomber that crashed after multiple engines failed during a training mission in 1950, reports the Vancouver Sun.

“I found this big thing underwater, huge, never seen anything like it before,” Smyrichinsky told the newspaper. “I came up telling all my buddies on the boat ‘Hey, I found a UFO. It’s really bizarre.’ And I drew a picture of it, because I didn’t have a camera.”

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A short time later, he told some fisherman about what he found and they suggested it could be the inactive Mark IV (a.k.a. Fat Man) nuclear bomb the plane’s crew got rid of before turning on auto-pilot and ejecting themselves. (The 5-ton, 10-foot, blimp-like bomb from the 1950 mission was filled with lead and TNT, not plutonium.)

Smyrichinsky said he then googled the 1950 incident, and found a photo of the bomb in sections, one of which looked exactly like what he found.

The thing he found was “bigger than a king-size bed”, perfectly flat on top with a rounded bottom and had a hole in the center just “like a bagel,” he told the BBC.

He then emailed Canada’s Department of National Defence, which replied his finding was of “keen interest” to them. Gizmodo reports the Canadian Navy is sending ships to follow up on Smyrichinsky’s finding.

The Royal Aviation Museum of Western Canada, which houses a replica of the bomb, writes that the accident in 1950 happened after ice formed on the wings of a B-36B bomber doing a training run from Alaska to Texas. To make matters worse, half of the plane’s engines caught fire. The crew had to leave the plane, so they jettisoned the bomb somewhere over the water, fearing that the TNT alone in the bomb was dangerous enough, even without nuclear material.

The museum writes in describing the incident: “Gripped by the Cold War mentality, the U.S. government immediately launched a massive effort to find the plane. The Royal Canadian Navy rescued the crew, but the plane was not discovered until 1953 when the U.S. Air Force was looking for a lost prospector from Texas. While flying over Northern British Columbia they stumbled across the wreckage of the lost bomber in the snow-covered mountains – hundreds of kilometres in the opposite direction from where it was supposed to crash.”