The water conditions were perfect — “beautiful, clear, green” — when Sean Smyrichinsky went diving last month off the north coast of British Columbia.

The 45-year-old Canadian had joined two friends for a three-week fishing expedition. Setting off on his own one day, Smyrichinsky went searching for sea cucumbers that their small crew could harvest the following day.

Using a DPV, or a diver propulsion vehicle, Smyrichinsky plunged 25 to 30 feet down into the bay.

Ahead of him, a mysterious object emerged.

“And I thought, what a cool rock formation,” he said. “It’s perfectly round.”

As he approached the formation, Smyrichinsky discovered it wasn’t a rock, but something that appeared man-made.

It was perfectly round, he noted, with circles and bowls “the size of basketballs” cut into it.

He rushed back to the surface to tell his friends, boat captain Richard Hamilton and fellow diver Chrissy Anderson, about the bizarre object he had spotted.

“When I came out of the water, I was pretty excited about the big weird thing that I found,” Smyrichinsky said. “I drew a picture of the thing that I had found on a napkin with my buddies.”

He presented the illustration to his friends. “It’s a UFO,” he declared.

They told him he was crazy.

Smyrichinsky hung onto the napkin anyway. He knew what he had seen.

In the evenings, he consulted with fellow divers and fisherman in nearby boats to try to corroborate what he had seen. All of them dismissed him.

It wasn’t until Smyrichinsky was preparing to go home when an “old-timer” at a local village took him seriously.

“We wound up in this little fishing village and we started to get some Internet,” he said. “And one of the guys said, ‘Hey, maybe you found that old bomb they lost.’ ”

“That old bomb,” the older fisherman explained, was from a U.S. Air Force B-36 bomber that had crashed over British Columbia in 1950.

The wreckage from the plane was discovered a few years later, in a remote location, but a Mark IV nuclear bomb that it had reportedly jettisoned ahead of time was never recovered.

Throughout the Cold War and for decades afterward, the whereabouts of the bomb remained a mystery. The crash was the subject of “Lost Nuke: The Last Flight of Bomber 075,” a book published this year by historian Dirk Septer.

“After years of silence, the United States finally admitted to losing its very first nuclear bomb; the incident was its first Broken Arrow, the code name for accidents involving nuclear weapons,” a summary for the book reads. “But was the bomb dropped and exploded over the Inside Passage, or was it blown up at the aircraft’s resting place in the mountains? This Cold War-era tale follows the last flight of bomber 075 and attempts to unravel the real story behind more than fifty years of secrecy, misdirection, and misinformation.”

As the fisherman was relaying this to Smyrichinsky, he said he ran an online image search for the “Mark IV.”

Pieces of one of the schematic drawings of the bomb looked like what he had seen underwater.

It “was like 50 miles from where the plane crashed,” Smyrichinsky said.

That night, he reached out through Facebook to a friend in the Canadian Air Force with a note that he knew sounded bizarre: He had been hunting for sea cucumbers but potentially found a Cold War-era nuclear bomb.

Now what?

His friend suggested he contact the Royal Canadian Navy, so he did.

“They called me right back,” Smyrichinsky said. “They were very excited about it.”

The Canadian Navy has since deployed a ship to explore the site of the crash and invited Smyrichinsky to join them — something that has particularly thrilled the diver, who usually lives in Courtenay, B.C., where he runs the Union Bay Diving shop.

“That’s the last thing I expected,” he said, adding that even the fishing expedition had been a “one-off” and his first time diving for sea cucumbers. “I’m pretty shocked. I’m pretty floored by this.”

Smyrichinsky’s discovery does match up with the location of the 1950 bomber crash, Maj. Steve Neta of the Canadian Armed Forces told CBC News.

Neta also told the news network that the lost bomb was a “dummy capsule” and is not likely a nuclear weapon.

“Nonetheless, we do want to be sure and we do want to investigate it further,” Neta told CBC News.

The Canadian naval ship should arrive later this week, and Smyrichinsky plans to join them later this month. He is unsure of what to expect, still hedging that the object may not be the missing bomb.

“I think every diver wants to find a pot of gold,” Smyrichinsky said. “But you never expect to see this or something like this.”

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