The U.S. official in charge of the response to the Gulf of Mexico oil spill said Sunday that the underwater well has been sealed permanently - five months after an explosion on an oil rig led to the worst oil spill in U.S. history.  

Retired Coast Guard Admiral Thad Allen declared the well "effectively dead," after final tests were conducted on a cement plug that permanently sealed the well four kilometers beneath the floor of Gulf of Mexico.

President Barack Obama said the sealing of the well is an important milestone.  In a statement released on Sunday, he stressed that his administration would do all that it can to ensure that the region recovers from the disaster.

Gulf residents from Texas to Florida are facing a wide range of challenges, and the sealing of the well is only one step in that process.

Many are struggling economically and some fishing grounds remain closed.

Shrimpers who can operate in Gulf waters are finding it difficult to sell their catch because of fears that seafood from the region is unsafe to eat.

Toney Dardar is a shrimper in Golden Meadow Louisiana. "I'm still stumped, where is the oil to begin with, where is this?  If it is mixed in the water, what is it going to kill?  I mean, what is it going to do?"

Others living along the Gulf coast say they are worried that there is a misperception that all the oil has been cleaned up and the recovery work is finished.

P.J. Hahn is a coastal development director for Plaquemines Parish in Louisiana. "Yeah, it gets you really upset when you come out here and you hear people saying the oil has been picked up, it's over, the spill is finished.  It's not finished.  We still got a lot of oil left out out here to pick up," he said.

The flow of millions of barrels of oil was shut off in mid-July after the well was capped.  Mud and cement were later pushed down through the top of the well and the cap was removed.

But the well could not be declared dead until a relief well was drilled and the ruptured well was sealed.

The disaster has also taken a toll on the massive oil company BP that owns the well.

The British firm already has paid more than $8 billion in cleanup costs and has promised to set aside another $20 billion for a victims' compensation fund.

The company might face tens of billions of dollars in fines a well as legal costs from pending lawsuits.

The BP oil spill has triggered civil and criminal investigations, and it has led to stepped up government scrutiny of the oil and natural gas industry - including a moratorium on deepwater oil drilling which is still in effect.