HOUSTON (Reuters) - The outer edge of a massive oil spill in the Gulf of Mexico washed up to wildlife refuges and seafood grounds on the Louisiana coast on Friday, as efforts redoubled to avert what could become one of the worst U.S. ecological disasters.
The last flight by a Coast Guard plane on Thursday had situated the thin surface "rainbow sheen" of the slick just 10 metres (33 feet) from the Pass-a-Loutre wildlife reserve in Louisiana. It seemed inevitable that some of the oil would reach shore, although the Coast Guard was awaiting information from its first Friday morning flight, a spokesman said.
Thousands of feet (meters) of protective booms were being deployed in a desperate effort to keep the worst of the oil from damaging vulnerable wetlands and eco-systems.
President Barack Obama pledged to "use every single available resource" to contain the 120-mile (193-km) wide oil slick and the U.S. military ratcheted up operations.
The leak from a ruptured oil well on the ocean floor off the coast of the southern state is pouring out crude oil at a rate of up to 5,000 barrels (210,000 gallons or 955,000 litres) a day, according to the National Oceanic and Atmospheric Administration -- five times more oil than previously thought.
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So far, efforts to stop the flow of oil have failed. If unchecked, it will take about 50 days for the leak to eclipse the 1989 Exxon Valdez spill in Alaska, the worst U.S. oil spill on record that sent 10.8 million gallons (49 million litres) of crude oil into Prince William Sound.
The accident, which happened after the rig exploded and sank last week, has ramifications for Obama's proposals for new offshore drilling permits. The White House said on Friday that no new drilling would be allowed until a review of the oil spill was conducted.
The escalating threat has deepened fears of severe damage to fisheries, wildlife refuges and tourism in Louisiana, Mississippi, Alabama and Florida.
The Gulf Coast and its marshlands are home to hundreds of species of wildlife, including manatees, sea turtles now about to nest, dolphins, porpoises, whales, otters, pelicans and other birds. The wetlands are also a stopover for millions of migrating birds now transiting through the area.
In addition, the Gulf is one of the world's most fertile seafood grounds, teeming with shrimp, oysters, mussels, crabs and fish. It supports a $1.8 billion industry second only to Alaska.
The spill could not have come at a worse time for wildlife as many animals are now breeding and nesting, while shrimp and fish are spawning. The local estuaries are the nursery grounds for the whole fish population in the area.
Louisiana Governor Bobby Jindal, whose state is still recovering from the ravages of Hurricane Katrina in 2005, declared a state of emergency and asked the Defence Department for funds to deploy up to 6,000 National Guard troops to help.
The spreading oil is reaching a fragile wildlife preserve in marshland at the edge of the Mississippi Delta, which experts said would seriously damage the ecology of the area and could be very difficult to clean up.
Homeland Security Secretary Janet Napolitano declared it "a spill of national significance," meaning that federal resources from other regions could be used to fight it.
Obama said London-based oil giant BP, the majority owner of the offshore well, was ultimately responsible for the cost of the clean-up, which has pounded BP's share price and those of other companies involved in the project.
Shrimp fishermen in Louisiana have filed a class-action lawsuit against BP, Swiss-based rig company Transocean Ltd, Halliburton and Cameron, accusing them of negligence. None of the companies had an immediate comment on the lawsuit.
The Navy said it was supplying the Coast Guard with inflatable booms and seven skimming systems to try to contain the oil.
In Mobile, Alabama, U.S. Coast Guard Captain Steve Poulin, said authorities were preparing for "shoreline impact", although it was not possible to predict exactly when.
"We have a booming strategy for coastal Mississippi, Alabama and the Florida Panhandle," Poulin said, adding that some 500,000 protection and containment booms were stockpiled along the coastline for deployment.
BP and the Coast Guard have mounted what the company called the largest oil spill containment operation in history, involving dozens of ships and aircraft.
BP admitted struggling to control the spill, which is 5,000 feet (1,525 metres) under the sea off Louisiana's coast, and appealed for help. It has asked the Pentagon for access to military imaging technology and remotely operated vehicles to try to help it plug the ruptured well.
Eleven workers are missing and presumed dead after the rig exploded 11 days ago.
There are signs the spill may be worse than one in 1969 off Santa Barbara, California, which prompted a moratorium on oil and gas drilling off the Pacific and Atlantic coasts -- a ban Obama has said he wants to modify.
Opponents of Obama's plan are moving to block more drilling.
Bill Nelson, a Democratic senator from Florida, said he was filing a bill to temporarily prohibit the administration from expanding offshore drilling, citing the risk of a potential "environmental and economic disaster" from the spill.
The Obama administration did not rule out imposing a pause in new deepwater drilling until oil companies can show they can control any spills.
Underwater robots failed to activate a cutoff valve on the ocean floor to stop the leak and BP is now hoping to cover the well with a giant inverted funnel that would capture the oil at the sea floor and channel it directly to a tanker ship at the surface. But that will take four weeks to put in place, by which stage over 150,000 barrels could have been spilled.
If the funnel does not work, BP will have to rely on stemming the flow by drilling a relief well, which would take two to three months.
The White House said Obama had been briefed on how the slick may interfere with shipping channels, which it said could affect tankers delivering petroleum to the U.S. market.
It was not immediately clear to what extent shipping in the Gulf could be affected. While the Mississippi is a major export route for U.S. grains and the region is a significant importer of crude oil, there were no reports of disruptions.
Shares in BP and Transocean continued to fall on Friday as investors feared a significantly higher cleanup cost. BP is down around 12 percent and Transocean down nearly 15 percent since the rig explosion on April 20.
The Louisiana Offshore Oil Port, which handles more than one million barrels a day of crude imports and is connected by pipeline to the biggest U.S. refining region, said it did not expect any effect on its operations, which remained normal.
Additional reporting by Joshua Schnyer and Rebekah Kebede in New York and Kelli Dugan in Mobile, Alabama; Writing by Christopher Wilson and Pascal Fletcher; Editing Sandra Maler