Cleanup of oil from the surface continued Thursday. A BP statement issued Thursday said there are 1,040 vessels and 24,700 personnel involved in the response.

BP has been using chemical dispersants to break up the oil slick into small droplets that can be digested by microbes. However, the U.S. Environmental Protection Agency Thursday asked BP to find a less toxic dispersant than the one BP currently uses.

Meanwhile, the Obama administration is asking BP to release more data about the spill, White House press secretary Robert Gibbs said Thursday.

As BP made progress with its oil-containment efforts, heavy, brown oil started seeping to Louisiana's precious marshes, which are home to rare birds, mammals and other marine life, while another edge of the escaping crude reached a powerful current that could take it to Florida and beyond.

Small amounts of light oil have reached coastal areas of Louisiana over the past several weeks, but nothing like the brown ooze from the spill that started coating Louisiana marshes Wednesday.

"This is the first time we've seen this much heavy oil this far into our wetland," Louisiana Governor Bobby Jindal said at a news conference Wednesday. "We know there's a lot more heavy oil behind it that hasn't made it to shore yet."

He called for the U.S. Army Corps of Engineers to grant an emergency permit for the state to dredge sand from barrier islands to create sand booms as another line of defense against the oil spill.

"If I had been standing up, I would have fell to my knees," Billy Nungesser, president of Plaquemines Parish, Louisiana, told The Washington Post about learning of the news. "It's our greatest fear."

The oil's landfall puts Gulf wildlife in danger, and brown pelican, Louisiana's state bird which was removed from the U.S. federal endangered species list only in November, is at particular risk because it dives beneath the water's surface to forage, experts said.

Also in harm's way are at least 12 Gulf species listed by the U. S. government as endangered or threatened, including birds, sea turtles and the sperm whale.

The "Deepwater Horizon" drilling rig, leased by BP, exploded and sank some 52 km off Venice, Louisiana, late last month, killing 11 workers and unleashing a massive oil spill.