VENICE, La. -- An oil spill that threatened to eclipse even the Exxon Valdez disaster spread out of control and drifted inexorably toward the Gulf Coast on Thursday as fishermen rushed to scoop up shrimp and crews spread floating barriers around marshes.
The spill was both bigger and closer than imagined -- five times larger than first estimated, with the leading edge just three miles from the Louisiana shore. Authorities said it could reach the Mississippi River delta by Thursday night.
''It is of grave concern,'' David Kennedy of the National Oceanic and Atmospheric Administration, told The Associated Press. ''I am frightened. This is a very, very big thing. And the efforts that are going to be required to do anything about it, especially if it continues on, are just mind-boggling.''
The oil slick could become the nation's worst environmental disaster in decades, threatening hundreds of species of fish, birds and other wildlife along the Gulf Coast, one of the world's richest seafood grounds, teeming with shrimp, oysters and other marine life.
The leak from the ocean floor proved to be far bigger than initially reported, contributing to a growing sense among many in Louisiana that the government failed them again, just as it did during Hurricane Katrina. President Barack Obama dispatched Cabinet officials to deal with the crisis.
Cade Thomas, a fishing guide in Venice, worried that his livelihood will be destroyed. He said he did not know whether to blame the Coast Guard, the federal government or oil company BP PLC.
''They lied to us. They came out and said it was leaking 1,000 barrels when I think they knew it was more. And they weren't proactive,'' he said. ''As soon as it blew up, they should have started wrapping it with booms.''
The Coast Guard worked with BP, which operated the oil rig that exploded and sank last week, to deploy floating booms, skimmers and chemical dispersants, and set controlled fires to burn the oil off the water's surface.
The Coast Guard urged the company to formally request more resources from the Defense Department. A BP executive said the corporation would ''take help from anyone.''
Government officials said the blown-out well 40 miles offshore is spewing five times as much oil into the water as originally estimated -- about 5,000 barrels, or 200,000 gallons, a day.
At that rate, the spill could easily eclipse the worst oil spill in U.S. history -- the 11 million gallons that leaked from the grounded tanker Exxon Valdez in Alaska's Prince William Sound in 1989 -- in the three months it could take to drill a relief well and plug the gushing well 5,000 feet underwater on the sea floor.
Ultimately, the spill could grow much larger than the Valdez because Gulf of Mexico wells typically hold many times more oil than a single tanker.