Brown pelicans and gulls fly in front of oil booms Friday along the shoreline at Pass a l‘Outre, La., where the Mississippi River meets the Gulf of Mexico. Wildlife in the region is vulnerable to the looming oil spill from last week’s collapse and spill of the Deepwater Horizon oil rig.

Mouth of the Mississippi River ? British Petroleum once downplayed the possibility of a catastrophic accident at an offshore rig that exploded, causing the worst U.S. oil spill in decades along the Gulf Coast and endangering shoreline habitat.

In its 2009 exploration plan and environmental impact analysis for the well, BP suggested it was unlikely, or virtually impossible, for an accident to occur that would lead to a giant crude oil spill and serious damage to beaches, fish and mammals.

At least 1.6 million gallons of oil have spilled so far since the April 20 explosion that killed 11 workers, according to Coast Guard estimates. One expert said Friday that the volume of oil leaking from the well nearly 5,000 feet below the surface could actually be much higher, and that even more may escape if the drilling equipment continues to erode.

“The sort of occurrence that we’ve seen on the Deepwater Horizon is clearly unprecedented,” BP spokesman David Nicholas told The Associated Press on Friday. “It’s something that we have not experienced before … a blowout at this depth.”

Amid increased fingerpointing Friday, efforts sputtered to hold back the giant oil spill seeping into Louisiana’s rich fishing grounds and nesting areas, while the government desperately cast about for new ideas for dealing with the growing environmental crisis. President Barack Obama halted any new offshore drilling projects unless rigs have new safeguards to prevent another disaster.

The seas were too rough and the winds too strong to burn off the oil, suck it up effectively with skimmer vessels, or hold it in check with the miles of orange and yellow inflatable booms strung along the coast.

The floating barriers broke loose in the choppy water, and waves sent oily water lapping over them.

“It just can’t take the wave action,” said Billy Nungesser, president of Louisiana’s Plaquemines Parish.

The spill — a slick more than 130 miles long and 70 miles wide — threatens hundreds of species of wildlife, including birds, dolphins and the fish, shrimp, oysters and crabs that make the Gulf Coast one of the nation’s most abundant sources of seafood. Louisiana closed some fishing grounds and oyster beds because of the risk of oil contamination.

BP’s 52-page exploration plan for the Deepwater Horizon well, filed with the federal Minerals Management Service, says repeatedly that it was “unlikely that an accidental surface or subsurface oil spill would occur from the proposed activities.”

And while the company conceded that a spill would impact beaches, wildlife refuges and wilderness areas, it argued that “due to the distance to shore (48 miles) and the response capabilities that would be implemented, no significant adverse impacts are expected.”

Robert Wiygul, an Ocean Springs, Miss.-based environmental lawyer and board member for the Gulf Restoration Network, said he doesn’t see anything in the document that suggests BP addressed the kind of technology needed to control a spill at that depth of water.

“The point is, if you’re going to be drilling in 5,000 feet of water for oil, you should have the ability to control what you’re doing,” he said.

Although the cause of the explosion was under investigation, many of the more than two dozen lawsuits filed in the wake of the explosion claim it was caused when workers for oil services contractor Halliburton Inc. improperly capped the well — a process known as cementing. Halliburton denied it.