VENICE, La. — President Barack Obama toured the staging area for response efforts to the Gulf Coast oil spill on Sunday, afterwards saying "we're dealing with a massive and potentially unprecedented environmental disaster."
Mindful of the political damage suffered by President George W. Bush for a slow response after Hurricane Katrina ravaged the same region, Obama defended his administration's actions, saying it had been preparing for the worst from "day one" even as it had "hoped for the best."
The president vowed that the administration, while doing all it could to mitigate the environmental and economic disaster, would require well-owner BP America to bear all costs.
"BP is responsible for this leak. BP will be paying the bill," Obama, with rain dripping from his face, said in Venice, a Gulf Coast community serving as a staging area for the response.
Earlier Sunday, the National Oceanic and Atmospheric Administration announced a much wider area — from Louisiana to parts of the Florida Panhandle — would be closed to commercial and recreational fishing for at least 10 days.
Scientists were sampling the waters, and the federal government said all seafood harvested so far appeared safe.
And Interior Secretary Ken Salazar told NBC that the potential environmental outlook is "a very grave scenario."
"A lot of oil could spread" since stopping the three leaks from the rig that blew up and then sank nearly two weeks ago could take three months, he told NBC's "Meet the Press".
Video: Obama tours area BP, which operates the well, was more optimistic, telling NBC's "TODAY" show on Sunday that a temporary fix — domes that will be placed over the leaks until they can be cut off — was nearly ready to be deployed. The domes will have piping to send the spewing crude up to tankers for collection.
"We're forecasting (it) to be complete in eight to ten days," Doug Suttles, BP's chief for exploration and production, said of the first dome.
There has been little success stemming the flow from the ruptured well on the sea floor by skimming the oil, burning it or dispersing it with chemicals.
Long tendrils of oil sheen made their way into South Pass, a major channel through the salt marshes of Louisiana's southeastern bootheel that is a breeding ground for crab, oysters, shrimp, redfish and other seafood.
Adding to the gloomy outlook were warnings from experts that an uncontrolled gusher could create a nightmare scenario if the Gulf Stream current carries it toward the Atlantic.
'Slow version of Katrina'
There is growing criticism that the government and oil company BP PLC should have done more to stave off the disaster, which cast a pall over the region's economy and fragile environment.
Venice charter boat captain Bob Kenney lamented that there was no boom in the water to corral the oil, and said BP was "pretty much over their head in the deep water."
"It's like a slow version of Katrina," he added. "My kids will be talking about the effect of this when they're my age."
Weather conditions were not helping. "We're going to have some pretty strong storms. These are just the worst conditions. When you have seas like that, you can hardly get the boats out, and the winds affect the aircraft," said Ken Graham, head of the National Weather Service office in New Orleans.
Critical questions lingered: Who created the conditions that caused the gusher? Did BP and the government react robustly enough in its early days? And, most important, how can it be stopped before the damage gets worse?
Whether that will work for a leak 5,000 feet below the surface is anyone's guess; the method has previously worked only in shallower waters.
Company spokesman Bill Salvin said Sunday that the first of three domes is nearly done. It's being built in Port Fourchon, La., by a company called Wild Well Control.
Another spokesman, Steve Rinehart, said the oil will flow into the chamber and then be sucked through a tube into a tanker ship at the surface.
BP did not build the containment devices before the spill because it "seemed inconceivable" the blowout preventer on the rig would fail, Rinehart said. The blowout preventer typically activates after a blast or other event to cut off any oil that may spill.
"I don't think anybody foresaw the circumstance that we're faced with now," he said. "The blowout preventer was the main line of defense against this type of incident, and it failed."
Video: Seafood industry scared The April 20 explosion of the Deepwater Horizon exploration rig killed 11 workers and the subsequent flow of oil threatens beaches, fragile marshes and marine mammals, along with fishing grounds that are among the world's most productive.
The Coast Guard conceded Saturday that it's nearly impossible to know how much oil has gushed since the blast, after saying earlier it was at least 1.6 million gallons — equivalent to about 2½ Olympic-sized swimming pools.
Even at that rate, the spill should eclipse the 1989 Exxon Valdez incident as the worst U.S. oil disaster in history in a matter of weeks. But a growing number of experts warned that the situation may already be much worse.
The oil slick over the water's surface appeared to triple in size over the past two days, which could indicate an increase in the rate that oil is spewing from the well, according to one analysis of images collected from satellites and reviewed by the University of Miami. While it's hard to judge the volume of oil by satellite because of depth, images do indicate growth, experts said.
"The spill and the spreading is getting so much faster and expanding much quicker than they estimated," said Hans Graber, head of the university's Center for Southeastern Tropical Advanced Remote Sensing. "Clearly, in the last couple of days, there was a big change in the size."
In an exploration plan and environmental impact analysis filed with the federal government in February 2009, BP said it had the capability to handle a "worst-case scenario" at the site, which the document described as a leak of 162,000 barrels per day from an uncontrolled blowout — 6.8 million gallons each day.
Slideshow: Wildlife threatened by oil Oil industry experts and officials are reluctant to describe what, exactly, a worst-case scenario would look like — but if the oil gets into the Gulf Stream and carries it to the beaches of Florida, it stands to be an environmental and economic disaster of epic proportions.
The well is at the end of one branch of the Gulf Stream, the warm-water current that flows from the Gulf of Mexico to the North Atlantic. Several experts said that if the oil enters the stream, it would flow around the southern tip of Florida and up the eastern seaboard.
"It will be on the East Coast of Florida in almost no time," Graber said. "I don't think we can prevent that. It's more of a question of when rather than if."
Coast Guard Adm. Thad Allen, appointed Saturday by Obama to lead the government's response, said no one could pinpoint how much oil is leaking because it is about a mile underwater.
"And, in fact, any exact estimation of what's flowing out of those pipes down there is probably impossible at this time due to the depth of the water and our ability to try and assess that from remotely operated vehicles and video," Allen said during a conference call.
Allen said a Friday test of new technology to reduce the amount of oil rising to the surface seemed to be successful. An underwater robot shot a chemical meant to break down the oil at the site of the leak rather than spraying it on the surface from boats or planes, where the compound can miss the oil slick.
From land, the scope of the crisis was difficult to see. About a half-dozen fishing vessels sailed Sunday morning through the marshes of coastal St. Bernard Parish in eastern Louisiana, headed for the Biloxi Wildlife Management area. The oyster and shrimp boats, laden with boom, hoped to seal off inlets, bayous and bays.
The real threat lurked offshore in a swelling, churning slick of dense, rust-colored oil the size of Puerto Rico. From the endless salt marshes of Louisiana to the white-sand beaches of Florida, there is uncertainty and frustration over how the crisis got to this point and what will unfold in the coming days, weeks and months.
The concerns are both environmental and economic. The fishing industry is worried that marine life will die — and that no one will want to buy products from contaminated water anyway. Tourism officials are worried that vacationers won't want to visit oil-tainted beaches. And environmentalists are worried about how the oil will affect the countless birds, coral and mammals in and near the Gulf.
"We know they are out there" said Meghan Calhoun, a spokeswoman from the Audubon Aquarium of the Americas in New Orleans. "Unfortunately the weather has been too bad for the Coast Guard and NOAA to get out there and look for animals for us."
Slideshow: Oil disaster in Gulf Fishermen and boaters want to help. But on Sunday, they were again hampered by high winds and rough waves that splashed over the miles of orange and yellow inflatable booms strung along the coast, rendering them largely ineffective.
Some locals wanted to act faster.
"I don't know what they are waiting on," said 57-year-old Raymond Schmitt, in Venice preparing his boat to take a French TV crew on a tour. He didn't think conditions were dangerous. "No, I'm not happy with the protection, but I'm sure the oil company is saving money."
As bad as the oil spill looks on the surface, it may be only half the problem, said University of California Berkeley engineering professor Robert Bea, who serves on a National Academy of Engineering panel on oil pipeline safety.
"There's an equal amount that could be subsurface too," said Bea. And that oil below the surface "is damn near impossible to track."
'They go KABOOM'
Louisiana State University professor Ed Overton, who heads a federal chemical hazard assessment team for oil spills, worries about a total collapse of the pipe inserted into the well. If that happens, there would be no warning and the resulting gusher could be even more devastating because regulating flow would then be impossible.
Video: Sizing up the fight "When these things go, they go KABOOM," he said. "If this thing does collapse, we've got a big, big blow."
BP has not said how much oil is beneath the seabed that Deepwater Horizon was tapping. A company source did confirm reports that it was tens of millions of barrels — a frightening prospect to many.
Obama has halted any new offshore drilling projects until regulations are in place with new safeguards to prevent another disaster.
In Pass Christian, Miss., 61-year-old Jimmy Rowell, a third-generation shrimp and oyster fisherman, worked on his boat at the harbor and stared out at the choppy waters.
"It's over for us. If this oil comes ashore, it's just over for us," Rowell said angrily, rubbing his forehead. "Nobody wants no oily shrimp."
The Associated Press and Reuters contributed to this report.