In mid-1679, out there somewhere in the waters of Lake Michigan, the first full-sized sailing ship to ever hit the waters of the Great Lakes vanished, taking with it every soul on board. The commander of the vessel — which had a carved griffin at its bow and was named the Griffin — was a Frenchman named Robert La Salle. He had wanted to take his 40-foot vessel from Green Bay to Niagara, so on September 18 of that year, he and a crew of six men fired a single cannon shot and set sail. It was “with a light and very favorable wind from the West,” a historical account says. “It has not been possible to ascertain since what course they steered.”

In the intervening years, rumor begat rumor. According to the Great Lakes Exploration Group, some thought Indians had captured the ship. Others thought a bad storm had felled the vessel. Others contended a mutiny had erupted, and the men made off with the ship’s booty. But despite such interest, explorers have not gotten any closer to the truth. The mystery of what some have dubbed the “holy grail” of Great Lakes shipwrecks has persisted.

That may have now changed. On a spring day in 2011, two Michigan treasure hunters named Kevin Dykstra and Fred Monroe from Muskegon were out on an “old fiberglass boat that wasn’t too leaky” looking for treasure. They were hunting for box cars. In the late 1800s, ferries carried box cars across the lake and one of them was rumored to have fallen into the water. In it, the stories went, was more than $2 million worth of Confederate gold coins. So as the men trawled the waters on that cool day, they flipped on a sonar device to scour the lake floor.

Then something caught Dykstra’s attention. “We were literally in the water for a couple of hours when we got a hit on the sonar,” Dykstra told WZZM. Monroe helped Dykstra get on his gear to dive into the 37-degree water. “When I was down there, I turned around and I was literally four feet from this shipwreck and I never saw it on my way down, so my return trip was quite fast.”

They hadn’t found treasure. But they had perhaps found something of greater historic significance. Dykstra snapped a series of pictures of the wreck, and “when we put them on the computer, we were surprised by what we saw,” he told the Washington Post Thursday night. “Our jaws just dropped, and we said, ‘That looks like the Griffin.'”

The proof: Unlike other shipwrecks, this one didn’t have any sign of modernity. “There’s no cables, no cabin and no smokestacks,” he told WZZM. “It almost looked like the empty hull of a large canoe, and there were no mechanical devices of any kind of the debris.”

Plus, one of the pictures he snapped showed what appeared to be a carved griffin etched into the front of the ship. “So it’s either a 100-to-1 odds that the front of the ship looks exactly like a griffin, and I don’t know how that can happen by coincidence,” he said.

Still, who could be sure? So over the next few years, Dykstra consulted with a number of experts about the prospective find before he decided to alert the public. “When we went public, we know it would be a popular story, but we didn’t think this many people would be interested in it.” For that reason, he said, they haven’t revealed the exact location of the find, citing concerns someone would set sail for that location to plunder the wreckage.

Now, Dykstra says he and state archaeologists, who he claims are certain it is a shipwreck, will venture out to the site to determine the discovery’s significance. “This is certainly something that the state of Michigan is interested in,” Michigan archaeologist Dean Anderson told the Muskegon Chronicle. “It’s a little too soon to say” whether it’s the Griffin, Anderson added. “But I wouldn’t rule out the possibility.”

Dykstra himself is already convinced. “Oh my goodness, look at those photos,” he told The Post. “And look at those carvings on it. … This is some compelling information.”