Undersea robots carefully placed a huge dome over an oil leak gushing from a sunken rig deep in the Gulf of Mexico yesterday as workers rushed to protect the fragile US coast and skim a massive slick from the sea.
Favourable weather is expected to keep the bulk of the estimated three million gallons of oil spreading across the Gulf away from shore in the coming days.
But with a thin sheen of oil already lapping against Louisiana's coastal islands, local leaders begged for more boom to protect fragile coastal wetlands.
"It'll be so much harder to clean up this oil if it gets into the marshes," said Governor Bobby Jindal.
The US Coast Guard, which is assisting in the recovery efforts for which British energy giant BP is responsible, cautioned that resources have to be used "strategically".
"There's not enough to completely boom off every piece of coastline for all four states," petty officer David Mosley told AFP.
"That's hundreds and hundreds of miles."
Hope hinges on whether the unprecedented effort to cap the massive leak some 1,500 metres below the surface because it will take three months to drill relief wells to stem the flow.
An estimated 210,000 gallons of oil has been gushing every day from a pipe ruptured when the BP-leased Deepwater Horizon spectacularly sank on April 22, two days after an explosion that killed 11 workers.
Once the 100-ton chamber has settled into the ocean floor, engineers can begin hooking up pipeline to funnel the crude up to a waiting barge.
If it works as designed, engineers say the dome should collect about 85 per cent of the oil.
The delicate procedure 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.
"This has never been done in 5,000 feet of water. It's a technology first. It works in three (hundred) to 400 feet of water. But the pressures and temperatures are very different here," BP's chief executive officer Tony Hayward warned on CNN.
"We cannot be confident that it will work."
Coast Guard Rear Admiral Mary Landry also tried to manage expectations, adding that "This is not the final solution".
Sheen from the massive crude spill has been washing ashore on the Chandeleur Islands, some 100 kilometres off Louisiana, forcing US officials last Friday to close a wildlife refuge there to minimise disturbance to nesting sea birds and to allow clean-up work.
The Breton National Wildlife Refuge, home to endangered species of brown pelican, least tern and piping plover, is one of the oldest in the country and spreads across almost 7,000 acres.
The National Oceanic and Atmospheric Administration (NOAA) meanwhile 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.