The origin of a group of barrel-shaped concrete blocks on the bottom of the ocean at Pickles Reef off Key Largo has baffled divers for decades.
Underwater archeologists have theorized that a ship transporting barrels of powdered cement either sank or was grounded on the reef and offloaded the barrels to get free. The cement hardened in the water.
The wooden containers deteriorated long ago, leaving behind the barrel-shaped remains of what's nicknamed the "Barrel Wreck."
Complicating the probe is the fact that Pickles Reef has had more than its fair share of run-ins with boats.
Roughly 27 boats have wrecked there, according to Brenda Altmeier, underwater archeologist with the Florida Keys National Marine Sanctuary.
A group of volunteer underwater archeologists with the Washington, D.C.-based nonprofit Maritime Archaeological and Historical Society, is diving and surveying the remains of the barrels and other wreckage on Pickles Reef.
One of them, Historical Society President Steve Anthony, will give a free lecture tonight at the Key Largo library on the unidentified Barrel Wreck.
The society is promotes awareness and appreciation of historic shipwreck preservation and the science of maritime archaeology. It has had divers researching in the sanctuary here since 2003, Altmeier said.
The group's field surveys are being conducted under permit from the sanctuary.
"We rely heavily on these organizations and enjoy working with them," Altmeier said. "We will guide them. We help them get funding. They are doing extremely important work."
The cement in the barrels could have been meant for Henry Flagler's railroad in the Keys, as tests have shown that it is from the same era.
An expert on cement -- who had been working on Fort Jefferson in the Dry Tortugas -- analyzed a sample at the behest of the sanctuary and society and determined it was from the early 1900s, when Flagler's project began, Altmeier and Anthony said.
In addition to the concrete barrel-shaped objects are large metal sheets and sections of a boat hull and framing, Anthony added. "The goal is to find parts that solve the mystery," he said.
Anthony's presentation will begin at 7 p.m. at the Key Largo library, 101485 Overseas Highway.