An environmental group connected to the fort posted a photo of the object on its Facebook page Wednesday but did not divulge its exact location on Oak Island.

The state's Underwater Archaeology Branch, which oversees coastal waters, is expected to offer an opinion.

"Archaeologists and other history experts have been to the site and/or seen photographs, trying to determine exactly what it is, cannon or pipe," the agency said in a statement. "Taking an up close look, it doesn't appear to have cannon characteristics."

But it's big enough to be one.

The cylinder is iron and measures 10 inches around and 6 feet long. The gap inside is 8 inches in diameter.

Opinions vary on what the structure may be. Some say it could be a very big pipe. Others like Oak Island's J.D. Shadduck think it's definitely a cannon.

Shadduck said he was fishing at Caswell Beach last Sunday when he spotted the object. His wife, Lori, later shared a photo on Facebook.

"It was my first time there fishing. The tide was low, so that's how I saw it," said Shadduck, who operates a tattoo business on the island. "It looks like a cannon to me."

Fort Caswell is in Brunswick County and was built on the eastern tip of Oak Island between 1826 and 1838. However, it wasn't put in full use until the Civil War, when it became an important Confederate defense.

The U.S. Army resumed control after Confederate troops abandoned it, and the fort stayed part of the military until after World War I.

Since 1949, it has been owned by an association of Baptist churches, which use the fort for various programs related to the ministry.