TIMBALIER ISLANDS, La. (AP) — Not just flora and fauna are getting caked in oil. So is the Gulf of Mexico’s barnacled history of pirates, sea battles and World War II shipwrecks.

The Gulf is lined with wooden shipwrecks, American-Indian shell midden mounds, World War II casualties, pirate colonies, historic hotels and old fishing villages. Researchers now fear this treasure seeker’s dream is threatened by BP PLC’s deepwater well blowout.

Within 20 miles of the well, there are several significant shipwrecks — ironically, discovered by oil companies’ underwater robots working the depths — and oil is most likely beginning to cascade on them.

‘‘People think of them as being lost, but with the deepsea diving innovations we have today, these shipwrecks are easily accessible,’’ said Steven Anthony, president of the Maritime Archaeological and Historical Society.

‘‘If this oil congeals on the bottom, it will be dangerous for scuba divers to go down there and explore,’’ Anthony said. ‘‘The spill will stop investigations; it will put a chill, a halt on (underwater) operations.’’

The wrecks include two 19th-century wooden ships known as the ‘‘Mica Wreck’’ and the ‘‘Mardi Gras Wreck.’’ The German submarine U-166 and ships sunk by other German submarines during World War II are within the spill’s footprint.

The Mica was a 200-year-old, two-masted schooner that sank sometime before 1850, according to a report by the Minerals Management Service. It was discovered about 2,500 feet deep in the Mississippi Canyon during work to lay a pipeline.

In 2002, the Mardi Gras wreck was discovered by oilfield workers in even deeper waters: About 4,000 feet down about 35 miles off the Louisiana coast. The wreck got its name from the pipeline project where the wreck was found: the Mardi Gras Gas Transmission System, a huge deepwater pipeline system.

Researchers with Texas A&M University believe the sunken ship may have been a gun runner or British trader during the War of 1812.

BP played a part in finding the U-166, a German U-boat sunk in World War II off the Louisiana coast. Then, as now, the Mississippi River was an important corridor for merchant shipping.

Crews surveying a pipeline project for BP and Shell in the Mississippi Canyon region came across U-166 in 2001. On July 30, 1942, the German submarine torpedoed the passenger-freighter Robert E. Lee, and then itself was sunk by depth charges from the Navy escort PC-566.

This week, oil washed ashore in the Florida Panhandle, where the USS Oriskany aircraft carrier lies off the coast of Pensacola, Fla. The Navy sank it in May 2006 to make an artificial reef. Sen. John McCain once flew bombing runs off the ship’s deck.

The tedious task of examining the wrecks for damage is beginning, though it’s uncertain whether BP will be held responsible for ruining underwater sites.

Dave McMahan, Alaska’s state archaeologist and an Exxon Valdez oil spill veteran, said federal environmental surveys and the courts would likely decide the matter.

‘‘I would say for the folks working on cultural resources — or any resource — document everything,’’ McMahan advised.

Archaeologists are fanning out to assess the spill’s effect. The Gulf shoreline is chock full of history and to a trained eye, the bounty springs out.

‘‘This is like Christmas Day for me,’’ said Courtney Cloy, an archaeologist mapping the Timbalier Islands, a barrier island chain on Louisiana’s central coast. ‘‘I am finding ceramics all over the surface out here.’’

The origin of the ceramics was unclear. Perhaps they washed in from a shipwreck just offshore. Or they might have come from a hotel or home that once stood on the badly eroded barrier islands.

For now, the Timbalier islands are safe: Oil contamination has been modest and cleanup crews are being kept at bay.

But archaeologists have grave concerns for other locations.

Oil has begun washing up on Pensacola’s beaches, where in 1886, Geronimo, the Apache warrior, was imprisoned in Fort Pickens, the largest of four forts built to defend Pensacola Bay.

On the Mississippi coast, Ship Island was the only deep-water harbor between Mobile Bay and the Mississippi River for 300 years; thousands of Europeans first set foot in North America there, earning the nickname Plymouth Rock of the Gulf Coast.

During the Civil War, Ship Island was Union Adm. David Farragut’s base of operations, where he successfully launched an attack on New Orleans in April 1862.

On Grand Terre Island, just west of the Mississippi River, archaeologists have found remnants of a colony set up by Jean Lafitte, the pirate who helped Andrew Jackson win the Battle of New Orleans.

Archaeologist hope to avoid the mistakes made during the Exxon Valdez cleanup.

‘‘We learned from Exxon Valdez that there were incidents of looting by cleanup workers, equipment being brought in, destroying the ground,’’ said John Rawls, marine archaeologist with Earth Search Inc., a firm hired by BP to do archaeological surveys.

In one incident, cleanup workers stumbled across a prehistoric Chugachmiut burial cave containing wooden artifacts.

‘‘Cleanup workers found the cave, which was unknown to archaeologists, and removed some of the bones and then called a supervisor,’’ McMahan said. He said Exxon security collected more of the bones and state troopers raked remains into a body bag and carted them away. ‘‘The site was pretty much trashed,’’ he said.

McMahan said cleanup workers need to be trained to be aware of their surroundings and to tread lightly on the landscape.

Archaeologists worry the push to clean the BP spill as fast as possible is causing damage. Bulldozers and dredges are being used to build barrier islands and erect sand dams, and thousands of workers are raking tar balls and crude off beaches.

‘‘Avoidance is No. 1,’’ Cloy said. ‘‘We want to keep our footprint on these sites as minimal as possible.’’