(CNN) -- A four-story containment vessel left Port Fourchon, Louisiana, on a barge Wednesday en route to the Gulf of Mexico's gushing oil well, where BP will attempt to lower the container onto a ruptured deep-water pipe in an unprecedented operation.
"If all goes according to plan, we should begin the process of processing the fluid and stop the spilling to the sea on Monday," Doug Suttles, BP's chief operating officer, said Wednesday.
But he added: "It's very complex, and it will likely have challenges along the way."
The hope is that the container will collect the leaking oil, which would be sucked up to a drill ship on the surface. If the operation is successful, BP plans to deploy a second, smaller dome to deal with a second leak in the ruptured pipe, the company has said.
The container will take roughly 12 hours to reach the well site, and getting the large structure into position could take several days, BP said. The technique has never been attempted at the depth of these leaks at some 5,000 feet, Suttles cautioned.
In the meantime, authorities battled the massive oil spill from the undersea gusher with sweat and fire Wednesday as patches of oil crept to within two miles of the Louisiana bayous.
Two specially equipped "burn rigs" set fire to patches of crude oil near the ruptured undersea well at the heart of the spill, a BP executive said Wednesday afternoon.
Thousands of volunteers, wildlife officials, idled fishermen and National Guard troops mobilized to string floating booms along the beaches and across the mouths of estuaries leading toward the Gulf.
The outer sheen of oil was reported to be very close to the Chandeleur Islands and the Mississippi River delta in southeastern Louisiana, Coast Guard Rear Adm. Mary Landry told reporters. And an oyster fisherman spotted a large patch of oil sheen near the border between St. Bernard and Plaquemines parishes, about 40 miles southeast of New Orleans, Plaquemines Parish President Billy Nungesser said.
"It's disturbing, but it's two miles away from shore, so it's not devastating," Nungesser said. He said authorities have conceded that the oil spill will reach the state's barrier islands, but, "we've got to keep it out of the marsh."
Landry said the heavier concentrations of crude remained further offshore, and the latest predictions from the federal government said the weather would keep it largely stationary for the next three days.
The 72-hour forecast shows winds shifting to the south and blowing about 10 to 15 knots (12-17 mph), which is likely to produce only "a little bit of movement on the fringes," said Charlie Henry of the National Oceanographic and Atmospheric Administration.
"Nothing's changing real fast this week," Henry said.
The oil stretched from Louisiana's Breton and Chandeleur sounds, on the northeast side of the Mississippi Delta, to about 60 miles off Pensacola, Florida, Wednesday afternoon.
The leaking well is spewing an estimated 210,000 gallons (5,000 barrels) of crude into the Gulf every day.
Booms, skimmers and chemical dispersants were being used to corral and break up the oil before it hits the sensitive wetlands of Louisiana or the beaches of Mississippi, Alabama and Florida farther east.
Suttles said controlled burns were being carried out at two locations near the heaviest concentrations of oil Wednesday afternoon, the first such attempt in a week. A previous attempt at a controlled burn destroyed about 100 barrels of oil on the surface of the water.
The efforts come amid rising concern that the oil could kill wildlife and damage livelihoods for thousands of people along in the Gulf states. Parish and state officials in Louisiana have enacted plans to keep the oil out of the marshes at the heart of the state's fishing industry and wildlife habitat.
"If it gets back into the backwaters, into the bayous, that's where we'll kill off the food chain," Nungesser told reporters. "That's where it will devastate southern Louisiana for years to come, and we will lose our heritage in the fishing industry."
The timing of the spill "couldn't be worse for the bird populations in this region," said Ken Rosenberg, a bird expert at Cornell University.
"It's peak nesting season for thousands of brown pelicans, which have just recently come off the endangered species list," he said Wednesday on CNN's "American Morning." It's also peak migration season for birds coming to the Gulf of Mexico from Central and South America, he added.
BP, which is responsible for containing and cleaning up the spill, has deployed thousands of gallons of chemical dispersants in an effort to break up the oil. But the dispersants are not necessarily a cure-all, Rosenberg warned.
"Dispersants are keeping the oil out in the water and down under the water," he said. "Almost certainly it's going to have major effects down in the water to the marine life and, ultimately, this is the same marine life on which the birds and animals on the surface are dependent.
"So just because we are not seeing oil washing ashore does not mean there aren't major effects happening out in the water," he said.
Interior Secretary Ken Salazar, whose Cabinet agency oversees national parks and offshore oil exploration, visited the scene Wednesday. He told reporters that federal authorities "continue to do everything we can" to keep pressure on BP, which is responsible for the cleanup, and to protect fish and wildlife in the threatened area.