Workers have lowered a huge dome over an oil leak gushing from a sunken rig deep in the Gulf of Mexico, as energy giant BP battles the slick lapping ashore on protected islands off the US coast.
The complex, unprecedented operation to drop the 90-tonne chamber about 1500m below the surface to cap the leak from the rig was expected to be completed late on Friday.
The dome is hovering just above the seafloor as the area is being prepared to receive it by robotic submarines, said officials at the joint command centre. They added that they hoped to lower it to sea floor today, but needed to finish preparing the surface.
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"This is a very large device and needs to be very precisely placed," BP spokesman Doug Suttles told reporters after the dome began its descent late on Thursday, adding that engineers would "swing it over and they had to precisely lower it over the top of the leak point".
"Over the weekend, we expect to connect that dome to the drill ship Enterprise and hopefully beginning of next week, we'll begin to start to evacuate the oil from the seabed up to the surface."
BP is racing to contain the leak, which is hemorrhaging about 200,000 gallons of oil a day into the Gulf of Mexico from the sunken Deepwater Horizon rig that exploded on April 20, killing 11 workers.
Officials cautious
The delicate operation is seen as the best hope to stave off the biggest US environmental disaster since the 1989 Exxon Valdez spill in Alaska, but officials remain cautious about whether it will work.
BP's chief executive Tony Hayward warned on CNN that such a task had never been attempted at this depth. "It (the dome) works in 300 to 400 feet of water. But the pressures and temperatures are very different here," he said.
"We cannot be confident that it will work."
Oil sheen from the crude spill has begun washing ashore on the Chandeleur Islands, about 100km off Louisiana, forcing US officials to close a wildlife refuge on Friday.
"The refuge closure is important to keep the public safe, to minimise disturbance to nesting colonial sea birds, and to allow personnel conducting cleanup operations and recovery efforts to work safely and efficiently," officials said in a statement.
The Breton National Wildlife Refuge, home to endangered species of brown pelican, least tern and piping plover, is one of the oldest in the US, and spreads across almost 2800 hectares.
Fishing ban
The National Oceanic and Atmospheric Administration, meanwhile, also extended the area closed to commercial and recreational fishing to 4.5 per cent of gulf waters, saying the fishing ban would remain in place until May 17.
News of the sheen reaching the islands raised new fears for the fragile ecosystem of Louisiana's wetlands and shores - home to vital spawning grounds for fish, shrimp and crabs, and a migratory stop for rare birds.
Commercial fishermen in the gulf harvested more than a billion pounds of finfish and shellfish in 2008, while it is also enormously popular with recreational fishermen.
BP is also spraying dispersants over the slick to break it up, and deploying thousands of booms to try to contain the spreading oil.
Amid concerns over the exact make-up of the chemicals being flushed into the waters, US officials said they produced a similar effect to dishwashing liquid.
"It's really designed to break down the oil," said Bob Perciasepe, deputy administrator of the Environmental Protection Agency.
"It does not make the oil disappear but it makes it into smaller and smaller particles that makes easier over the long haul to be biodegradable instead of big ... really, oily globs."
More booms needed
Louisiana governor Bobby Jindal joined local officials in begging for more booms to be deployed along the coast instead of supplying them to Florida and Alabama, where the danger is less imminent.
"We continue to call on the Coast Guard and BP for additional hard boom - it'll be so much harder to clean up this oil if it gets into the marshes," he told a news conference in the remote port of Hopedale after touring the slick.
Political reaction to the spill also intensified as a high-powered US Republican senator warned that action on legislation to fight climate change was now "impossible" due to fierce new opposition to offshore drilling in the wake of the disaster.
"I believe it would be wise to pause the process and reassess where we stand," Senator Lindsey Graham said.
