BP capped one of three leaks at the well Tuesday night, a step that will not cut the flow of oil but that BP has said will make it easier to help with the gusher.
Two satellite images taken Wednesday morning indicate oil has reached the Mississippi Delta and the Chandeleur Islands off the coast of Louisiana.
It's not clear whether the oil is on shore, but it's very close, said Hans Graber, director of the University of Miami's satellite sensing facility.
U.S. Coast Guard Lt. James McKnight said crews remained at the Chandeleurs on Wednesday after officials got a report of oil coming ashore, but they have not located it.
"They're sitting there, basically, waiting for the first signs of any kind of a sheen to touch the islands," he said.
Graber said the images also show oil drifting south, toward the Loop Current, which scientists say could carry it toward Florida and the Florida Keys. The northern edge of the current may have already picked up some oil.
Florida officials fearing tourists will cancel their vacations are trying to quash rumors that oil is already washing up on beaches there.
"We are not two or three days away from it hitting the shore," said David Halstead, Florida's emergency management chief. "The beaches are still open."
The long-term effects of the spill on wildlife are not yet clear. Dead endangered turtles have been washing up on Gulf Coast beaches, but they have no signs of oil and federal fisheries officials are investigating whether aggressive shrimpers may have killed them.
Efforts to stop the oil before it gets to shore picked up Wednesday. Coast Guard crews said they were preparing to corral some and set it on fire, which they last tried April 28. A 28-minute burn then removed thousands of gallons, but weather had not allowed them to do it again. Waves and wind were calm Wednesday.
In Plaquemines Parish, near the southern tip of Louisiana, officials loaded absorbent boom shortly after dawn to take out to the mouth of the Mississippi River. The barge will be used as a distribution point for local fishermen to lay the boom around sensitive marshes.
At a nearby marina, local shrimpers planned to use their boats to put down boom as part of a program BP is running.
The Coast Guard said officials planned to send out about 80 vessels from Biloxi and Pascagoula, Miss., and Orange Beach, Ala., primarily to handle booming. Two Coast Guard cutters would also conduct offshore skimming operations. Crews in Mississippi are picking up debris from beaches to make cleanup easier if oil comes ashore.
In all, about 7,900 people are working to protect the shoreline and wildlife, and some 170 boats are also helping with the cleanup.
A rainbow sheen of oil has reached land in parts of Louisiana, but forecasts showed the oil wasn't expected to come ashore for at least a couple more days.
"It's a gift of a little bit of time. I'm not resting," Coast Guard Rear Adm. Mary Landry said.
In their worst-case scenario, BP executives told members of a congressional committee that up to 2.5 million gallons a day could spill if the leaks worsened, though it would be more like 1.7 million gallons. In an exploration plan filed with the government in February 2009, BP said it could handle a "worst-case scenario" it described as a leak of 6.8 million gallons per day from an uncontrolled blowout.
Containment boxes have never been tried at this depth -- about 5,000 feet -- because of the extreme water pressure. If all goes well, the contraption could be fired up early next week to start funneling the oil into a tanker.
"We don't know for sure" whether the equipment will work, BP spokesman Bill Salvin said. "What we do know is that we have done extensive engineering and modeling and we believe this gives us the best chance to contain the oil, and that's very important to us."
The rig was owned by Transocean Ltd. Some of the surviving workers who were aboard when it exploded are suing that company and BP PLC. In lawsuits filed Tuesday, three workers say they were kept floating at sea for more than 10 hours while the rig burned uncontrollably. They are seeking damages.