A diver inspects a beam found in Lake Michigan. Experts are wondering if it’s part of a boat that sank in 1679. (David J. Ruck/Associated Press)

A wooden beam that was stuck in the bottom of northern Lake Michigan may be part of a French ship that disappeared more than 300 years ago.

Archaeologists exploring the site this week said the beam appears to have been there for centuries.

Expedition leaders had hoped to find that the beam was attached to the long-lost Griffin. That ship, commanded by the French explorer La Salle, wasn’t seen again after setting sail in September 1679 from an island near the entrance of Green Bay, in what is now northern Wisconsin.

Michel L’Hour, a French archaeologist and shipwreck expert, said the timber appears to be a bowsprit, a pole that extends from a vessel’s stem.

But as an excavation team dug into the lake bed, the 19-foot beam came loose, revealing that it was attached to nothing.

No other wreckage has been found, but project manager Ken Vrana said there’s still a chance the ship is nearby. With the timber no longer in place, crews stepped up their digging operation in hopes of reaching a hard surface that a probing device indicated is 18 to 20 feet below the lake bed.

“We have found a floor under that exposed wooden timber,” said Vrana, the project manager. “We have more excavation to do before verifying what that surface is.”

Steve Libert, a shipwreck enthusiast who has searched three decades for the Griffin, discovered the timber in 2001 and recently obtained permits to explore beneath the muddy surface.

— Associated Press