Mourners bowed their heads at vigils Wednesday to mark the first anniversary of the massive blowout on BP's Deepwater Horizon rig, which unleashed the biggest maritime oil spill in history and blackened beaches from Texas to Florida.

President Barack Obama vowed to do "whatever is necessary" to restore the US Gulf Coast and to "hold BP and other responsible parties fully accountable for the damage they've done and the painful losses that they've caused."

Oil-coated dolphin carcasses and sticky tar balls continue to wash up on beaches a year after the April 20, 2010 explosion which killed 11 workers and sank the Deepwater Horizon some 50 miles (80 kilometers) off the coast of Louisiana.

By the time the well was capped 87 days later, 4.9 million barrels (206 million gallons) of oil had gushed out of the runaway well 5,000 feet below the surface of the Gulf of Mexico.

Hundreds of miles of fragile coastal wetlands and beaches were contaminated, a third of the Gulf's rich US waters were closed to fishing, and the economic costs have reached into the tens of billions.

Months of uncertainty caused deep emotional trauma for the fishermen and coastal residents who feared their way of life was being destroyed. More than 120,000 people are waiting on compensation claims inching through a clogged system.

"I was very happy, and to have it ripped away from you, it's like a part of your heart is dead," said shrimper Dee Poche of Lafitte, Louisiana.

The immediate environmental damage appears to be surprisingly limited -- thanks in large part to favorable winds and tides which kept the bulk of the oil from reaching the coast -- but scientists warn it's far too soon to predict what the full impact will be.

"While we've made significant progress, the job isn't done," Obama said in a statement.

Nearly 2,000 workers remain engaged in the recovery effort -- down from a peak of more than 48,000 at the height of the spill -- and the goal is to "ensure that the Gulf Coast recovers stronger than before," Obama said.

The administration has also implemented "aggressive new reforms for offshore oil production in the Gulf so that we can safely and responsibly expand development of our own energy resources," he added.

The spill exposed the industry's shocking lack of preparedness, weak safety culture and dangerously lax government oversight.

"This disaster was almost the inevitable result of years of industry and government complacency and lack of attention to safety," a presidential commission tasked with investigating the spill concluded.

But the Obama administration's solution - a temporary moratorium until new safety rules could be implemented - was slammed by residents and politicians for dealing Louisiana a bigger economic blow than the spill.

"When we have other tragedies - when we have airlines that crash, we don't shut down the airline industry," Louisiana Governor Bobby Jindal said Wednesday as he urged federal regulators to speed up the permitting process and let drilling rigs get back to work.

"We want more domestic oil production. We obviously want it to be done safely," Jindal said at a press conference in the hard-hit beach town of Grand Isle.

"The less drilling that happens over here, all that means is more money going overseas to countries that aren't necessarily friendly to us."

But activists at a candle-light sunrise vigil in New Orleans said the disaster should be a catalyst for moving the country towards greater use of alternative energy sources.

"The only way to protect our communities, our waters and our air from another disaster is to break our addiction to oil and embrace a cleaner, safer energy future for America," said Sierra Club president Robin Mann.

"We must not allow the lives lost in the BP disaster to be in vain," she said after a prayer service.

"Recovery on the Gulf, the health of our economy, and the safety of all Americans depends on action now."

The spill was almost 20 times bigger than the one caused by the 1989 Exxon Valdez tanker disaster and is surpassed only by a 1910 gusher in California and deliberate releases by Iraqi troops during the 1991 Gulf War.

BP took a $40.9 billion loss in 2010 related to the spill, including $13.6 billion for the initial response, and hopes to recover a significant portion of the cost from its well ownership partners and from subcontractors Transocean, which ran the drilling rig, and Halliburton, which was responsible for the well's flawed cement job.

It has set up a $20 billion trust fund to cover compensation claims from fishermen and others affected by the spill, but also faces massive fines and penalties from the US government and will be responsible for repairing the environmental damage.

Transocean - which recently came under heavy fire for awarding executives big safety bonuses - flew the relatives of those who died on the drilling rig out to the site of the disaster in a solemn memorial.

earlier related report
Timeline of Gulf of Mexico oil spill
New Orleans, Louisiana (AFP) April 20, 2011 - The worst maritime oil spill in US history began a year ago Wednesday when an explosion ripped through a BP-licensed rig in the Gulf of Mexico, killing 11 men drilling a well 5,000 feet (1,500 meters) below on the sea floor.

The well gushed oil into the gulf for three months before it was capped, but the impact on the economies, environments and residents of US Gulf Coast states continues to be felt.

Here is a summary of events since the start of the disaster:

April 2010

-- 20: The BP-leased Deepwater Horizon oil rig explodes some 50 miles (80 kilometers) off the coast of Louisiana. Eleven rig workers are killed.

-- 22: The rig sinks to the sea floor.

May 2010

-- 2: President Barack Obama visits Louisiana and says BP is clearly "responsible" for the spill and must pay for the clean-up.

The US government bans commercial and recreational fishing in parts of the Gulf.

-- 6: BP tries lowering a 100-ton containment dome on top of the gushing well. The effort fails.

-- 12: A new attempt to cap the oil flow using a smaller containment dome also fails.

-- 20: Officials in Louisiana confirm that oil has reached the state's shore and "destroyed" miles of fragile marshland.

-- 22: Obama forms an independent commission to probe the spill.

-- 27: Obama announces a six-month moratorium on deepwater drilling.

-- 30: BP chief executive Tony Hayward sparks outrage when he says "I would like my life back."

June 2010

-- 1: The US launches a civil and criminal investigation into the spill.

-- 2: US officials extend the fishing ban, to cover more than a third of the Gulf's federal waters.

-- 10: BP says it has spent $1.43 billion on spill response, containment, relief-well drilling and claims.

-- 15: Ratings agency Fitch slashes BP's rating to close to junk.

-- 16: BP announces a $20-billion fund to compensate people affected by the disaster.

July 2010

-- 12: A giant cap is placed successfully over the leak.

-- 15: BP announces oil has stopped flowing into the Gulf.

-- 27: BP chief Hayward resigns, replaced by American Bob Dudley.

August 2010

-- 2: US says the ruptured well gushed 4.9 million barrels of oil into the Gulf, of which 800,000 barrels were captured.

-- 5: A "static kill" operation plugs the well with heavy drilling mud and cement.

September 2010

-- 19: US officials declare the well "dead" after permanently sealing off the reservoir.

October 2010

-- 13: The US lifts the moratorium on deepwater drilling.

January 2011:

-- 11: In its final report, the presidential commission probing the spill says the disaster was "foreseeable and preventable." It calls for overhaul of oil and gas industry practices and tougher government oversight.

February 2011

-- 1: BP posts a $4.9-billion loss for 2010 and warns that the $40.9-billion charge related to the spill does not include many potential legal liabilities.

-- 28: The US government awards its first new permit for Gulf deepwater drilling to US firm Noble Energy.

April 2011

-- 19: US authorities open all federal waters that had been closed to fishing due to the oil spill.

-- 20: Obama vows to do "whatever is necessary" to restore the Gulf Coast.