Placing the metal containment device is the first step in a laborious process that could easily go awry, experts had warned. "This is going to take a few days ... and it may or may not work," said Coast Guard Rear Adm. Mary Landry.
If it does work, the four-story dome won't shut down the fountain of crude spurting from a broken pipe on the muddy gulf floor. "This is not the final solution," Landry said earlier. But it could capture most of the oil and funnel it 5,000 feet upward to a waiting ship.
As it happened, a large volume of hydrates -- icelike crystals that form when gas combines with water -- accumulated inside the vessel, a BP official said Saturday.
The dome was moved off to the side of the wellhead and is resting on the seabed while crews work to overcome the challenge, a process expected to take at least two days.
Suttles said the gas hydrates are lighter than water and, as a result, made the dome buoyant. The crystals also blocked the top of the dome, which would prevent oil from being funneled up to a drill ship.
"We did anticipate hydrates being a problem, but not this significant [of one]," he said.
Two options officials are looking at to resolve the problem are heating the dome or adding methanol to dissolve the hydrates, Suttles told CNN, adding that they are continuing to assess other methods to capturing the oil.
The crude is leaking at a rate of 210,000 gallons (5,000 barrels) a day.
Suttles said that another possible solution would be to "take ground-up material of various types and try to inject it into the blowout preventer at the bottom of it and it will flow up and plug it up."
The blowout preventer is a 48-foot-tall, 450-ton apparatus that sits atop the well 5,000 feet underwater. It would stop the leak, BP has said, but it has not been working properly since the Deepwater Horizon oil rig exploded in flames on April 20 and sank two days later, triggering an oil spill that President Obama has called a "potentially unprecedented environmental disaster."
On the surface of the Gulf of Mexico, the Coast Guard will continue efforts to disperse and contain the massive oil slick that has started to reach Louisiana's outer islands.
The Coast Guard performed four controlled burns, dropped 28,000 gallons of dispersant chemical and skimmed 8,000 barrels of an oil-water mix on Thursday, Petty Officer Brandon Blackwell said.
The oil rig caught on fire April 20 and sank two days later about 50 miles off southeastern Louisiana. Eleven missing workers are presumed dead.
The untapped well is gushing about 210,000 gallons, or 5,000 barrels, of oil a day into the Gulf of Mexico, according to BP and government estimates.
BP this week capped one of the three points where the oil is pouring out, a pipe that is smaller than the main wellhead.
The National Oceanic and Atmospheric Administration enlarged the boundaries of its no-fishing zone in federal waters to reflect the growing spill and extended the restrictions to May 17. But the agency said the vast majority of gulf waters remain unaffected by the disaster.
Three teams were sent to inspect the Chandeleur Islands, where a sheen of oil has washed up, potentially contaminating parts of the second-oldest wildlife refuge in the national system.
Oil first made landfall on the crescent-shaped chain Wednesday. By Friday morning, the effects were evident in lapping oil and a distinct lack of birds, said Capt. Mark Stebly, a fishing guide who has lived on one of the islands for 25 years.
The refuge is a breeding ground for thousands of birds, including brown pelicans. Hundreds of frigate birds large dark seabirds with the longest wingspan, in proportion to their weight, of all birds roost in the mangroves .
The stakes are high for residents of coastal Louisiana who make their living from fishing in the Gulf. "It's killing everybody down here, everybody is more or less getting ulcers worrying about this, and it's something we experienced five years ago with [Hurricane] Katrina," charter boat owner Tom Becker said. "But we knew it was coming faster than this thing is and we don't know what the long-term effect of what's going to happen with this if it [the oil] does get up here."