On shallow Pickles Reef, 3 ½ miles off the shore of Key Largo, the sun lit up a mishmash of metal, iron and barrel-shaped cement artifacts that have been commingling with colorful coral and tropical fish for a century or more.

As two curious spotted eagle rays cruised by, a group of divers from the Washington-based Maritime Archaeological and Historical Society surveyed the unidentified wreckage that hurricanes, tropical storms and strong currents have scattered over a site larger than a football field.

“Mother Nature has a way of mixing it up in a soup that is hard to sort out what we have,” the society’s president, Steven Anthony, said during a June trip to the Keys. “We are trying to put all that puzzle back together, like putting back together Humpty Dumpty, to solve the mystery.”

Is the submerged debris field primarily a single wreck, perhaps one of the 23 ships with names that include Lion, Mimi, S.S. Oxford and Hope of London that Key West Admiralty court records document as sunk, abandoned, lost or wrecked on that reef in the 1800s? Or is it the remnants of several wrecks, from different eras?

And are the numerous cement cylinders even connected to the wreckage? Or was it cargo a boat’s crew offloaded to lighten the load enough to get off the treacherous reef, which at some points is less than 10 feet deep?

“We don’t know, but we have enthusiastically been trying to pin this wreck down for a number of years now,” said Brenda S. Altmeier, program support specialist with the Florida Keys National Marine Sanctuary — in which the wreck site is located.

Over the last few decades, the prevailing story told to divers and snorkelers has been that the wreck is that of a Civil War-era ship or barge that was carrying cement destined to Key West for the construction of Fort Jefferson or the Martello Towers.

But that story was debunked in 2008 after a New York laboratory’s analysis of the cement positively identified it as Portland cement, produced no earlier than 1890 and only until 1925.

“This information leads us down a different trail of bread crumbs,” Altmeier said. “We can eliminate the Civil War era ships.”

One of the new theories it that the vessel was carrying cement for construction of the Key West Extension of the Florida East Coast Railway. The maritime society located a 1908 picture of construction of a Henry Flagler railroad bridge that clearly shows neat rows of barrels that appear similar to the shape of the cement features at the bottom of Pickles Reef. Workers also appear to be pouring concrete next to the barrels. But so far, it’s just a theory.

With so few government resources, and 68 priority shipwreck sites to identify just in the Upper Keys, Altmeier says the sanctuary welcomes the help of enthusiastic private groups like the Maritime Archeological and Historical Society, providing them with permits and previously gathered information.

The society began to investigate the site at Pickles Reef in 2010, at the request of Florida State Underwater Archaeologist Roger Smith. The group has returned each year since, gathering more clues both underwater and on land, working with local historians and combing through archives.

Originally, Anthony said, the group wasn’t convinced it was the site of a shipwreck. “It looks like a big debris field and we thought it could be machinery and maybe offloaded salvage,” he said.