For four days, the spill from a collapsed oil platform off the coast of Louisiana was believed to have been contained.
But now, officials confirm the undersea well is leaking and a sheen of oil stretches for 1,800 square miles, threatening the coastlines of four states.
Officials now say it could take months to stop the leaking, which could potentially wreak major environmental damage to the surrounding area.
"We are in a very serious situation," said Rear Adm. Mary Landry of the Coast Guard. "Forty-five to 90 days is the initial estimate. That's an estimate right now before this well could be secured."
This comes less than a week after Landry told ABC News that "We've been able to determine that there is nothing emanating from the wellhead."
Though there is still no leak from the wellhead, there is a leak in the pipeline that led to the rig, and that is a big problem.
Some 42,000 gallons a day are gushing out right now and should the well itself open, 100 times more crude could spew into the water.
The Gulf of Mexico's ecosystem, which includes shrimp, fish, birds and coral, could become endangered. And that could take a huge toll on the lucrative seafood industry in this area.
Oil has been leaking since April 22, when the oil rig sunk, two days after the Deepwater Horizon rig exploded about 50 miles off the Louisiana coast. Eleven workers are missing and, at this point, believed dead.
Fortunately, this 400-square-mile lake of crude and sheen is nearly stagnant It's moving sluggishly toward the coast, at 1 mile per hour.
As of Sunday, the spill was still about 70 miles from the mainland. But it is inching closer to a chain of islands called the Chandeleurs, which are part of a wildlife refuge that hosts pelicans and other seabirds.
The Coast Guard and BP, owner of the sunken rig, intend to dispatch a fleet of 32 cleanup ships to scoop up the slime.
When the burning rig sank, its 5,000-foot pipeline crumbled like a giant broken straw. The biggest leak has been found at the first crook. The well valve is holding for now, but there's at least one more leak. BP is dispatched a squadron of underwater robots to work on repairing those leaks and to ensure the well valve remains closed. But so far that hasn't worked.
Today, BP is moving in another mobile rig.
Similar to the one that exploded Tuesday, this oil rig will also drill a well. Then, acting like a bendable straw, it will cut a diagonal path toward the damaged well, essentially corking it shut with chemicals.
BP is also constructing a dome that would be lowered to cover the wellhead and then bring the oil to the surface so it can be collected. The dome system has been effective in shallow water, but has never been tried this deep.
If that doesn't work, BP will drill a relief well near the original one, use it to pump mud and rocks into the old well until it stops leaking. But that could take months.
But this is a stopgap effort; the only surefire way of stopping the leak is plugging the well through a relief well.
For more on this story tune in to "World News With Diane Sawyer" at 6:30 p.m. ET.
The Associated Press contributed to this report.