HOUSTON The U.S. Coast Guard said on Wednesday five times as much oil as previously estimated was leaking from a well beneath the site of a deadly drilling rig explosion as the slick threatened wide-scale coastal damage for four U.S. Gulf Coast states.
The Coast Guard said that London-based BP Plc -- the owner of the well who is financially responsible for the cleanup -- found a third leak in a well 5,000 feet (1,525 metres) under the sea off Louisiana's coast.
"BP has just briefed me of a new location of an additional breach in the riser of the deep underwater well," Coast Guard Rear Admiral Mary Landry, who is heading the federal cleanup effort, told reporters at a briefing.
Eleven workers are missing and presumed dead after the worst oil rig disaster in almost a decade.
Swiss-based Transocean Ltd's Deepwater Horizon rig sank on April 22, two days after it exploded and caught fire while it was finishing a well for BP Plc about 40 miles (64 km) southeast of the mouth of the Mississippi River.
President Barack Obama has been briefed on the situation, and "we have urged BP to leverage additional assets," including possible help from the U.S. Defence Department, Landry said.
The oil slick threatens coastal wildlife refuges, pristine beaches and estuaries in Louisiana, Mississippi, Alabama and Florida.
The leak is now estimated at 5,000 barrels per day -- five times than previously estimated.
The leaking well has already created an oil sheen and emulsified crude slick slightly bigger than the U.S. state of West Virginia, which BP and the Coast Guard are scrambling to contain before it reaches land.
LARGEST CONTAINMENT IN HISTORY
BP and the Coast Guard have already mounted what BP has called the largest oil spill containment operation in history, involving dozens of ships and aircraft.
After underwater robots failed to activate a cutoff valve on the ocean floor to stop the leak, BP and the Coast Guard on Wednesday set a "controlled burn" to battle a giant oil slick and prevent it from growing.
"We will not rest until we have done everything to bring this under control," said Andrew Gowers, head of group media for BP, likening the spill's consistency to "iced tea" with the thickness of a human hair.
By Wednesday afternoon, the edge of the spill was 23 miles (37 km) off the Louisiana coast, near fragile estuaries and swamps teeming with birds and other wildlife. A shift in winds could push the spill inland to the Louisiana coast by this weekend, according to forecasters at AccuWeather.
Tarballs and emulsified oil streamers could reach the Mississippi Delta region late on Friday, said Charlie Henry, an expert with the National Oceanic and Atmospheric Administration.
Along with a large seafood industry, the area contains key wildlife habitats in the Pass-A-Loutre Wildlife Management Area and Breton National Wildlife Refuge on the Louisiana coast, which are teeming with nesting birds.
The spill could be devastating for fishermen and oystermen that rely on estuaries and swamps along the Mississippi River for their livelihood.
"We're sitting here half praying and half with our fingers, toes and everything else crossed," said Byron Encalade, president of the Louisiana Oysterman Association in Pointe A La Hache, who lost five boats when Hurricane Katrina hit in 2005.
As the oil spill grows, so does the chance that it will affect efforts by the U.S. Congress and Obama to open more offshore areas to limited oil and gas drilling.
"This brings home the issue that drilling despite all the advancements in technology is still a risky business," said Athan Manuel of the Sierra Club, an environmental group.
Preparations were underway to deploy thousands of feet (km) of floating booms in Louisiana, Mississippi, Florida and Alabama in an attempt to contain the oil slick, the Coast Guard said.
The Louisiana accident is the worst oil rig disaster since 2001, when a rig operated by Petrobras off the Brazilian coast exploded and killed 11 workers.
So far the spill is not nearly as big as the Exxon Valdez disaster, which spilt about 11 million gallons (50 million litres) of oil into the Prince William Sound in Alaska in 1989. BP's well is spewing about 210,000 gallons (954,500 litres) of oil a day into the ocean, the Coast Guard estimates.
(Additional reporting by Kristen Hays in Houston and Pascal Fletcher in Miami; Editing by Mary Milliken and Sandra Maler)