That makes it the largest oil spill in the state's history and the biggest since the Exxon Valdez crashed off the coast of Alaska in 1989.
The oil, released from ruptured pipelines, sunken boats and disabled refineries, along with toxic chemicals from industrial plants, bacteria from damaged sewage systems and small amounts of lead and arsenic, flowed into ground water, drinking water and the Gulf of Mexico.
In Louisiana, Mississippi and Alabama, the storm flooded five Superfund sites, severely polluted industrial sites scheduled for federal cleanup, releasing some of the nation's worst toxic materials.
Parts of the infamous "cancer alley," an industrial corridor along the Mississippi River between New Orleans and Baton Rouge, also flooded, leading to speculation about the number and types of toxic chemicals that may have been leaked by hundreds of industrial facilities in the area, USA Today reported.
"The range of toxic chemicals that may have been released is extensive," Lynn Goldman, an environmental health sciences professor at Johns Hopkins University, told the newspaper in a Sept. 14 report. "We're talking about metals, persistent chemicals, solvents, materials that have numerous potential health impacts over the long term."
The Environmental Protection Agency called the flooding and contamination the biggest disaster the agency has ever had to handle.
"We heard that the degree of environmental damage is considered catastrophic," Sen. James Jeffords, I-Vt., said after a briefing with EPA Administrator Stephen Johnson soon after the storm.
Despite the troubling initial estimates, just how lasting an environmental impact on the Gulf Coast Hurricane Katrina will have has yet to be determined. Much of the oil has been cleaned up, according to the Coast Guard, but environmentalists say the untold damage could have severe long-term effects.
A report from the Natural Resources Defense Council said Gulf Coast wetlands, home to commercial fisheries and wildlife, are among Earth's most sensitive ecosystems and oil spilled close to the shore could "linger for decades."
"This is probably the single largest environmental catastrophe that we're aware of in the U.S.," said Erik Olson of the NRDC. "It's hard to really get your mind around the extraordinary impacts."
According to Olson, although the Coast Guard says the oil is gone, where it's going is not being discussed.
"What they say is most of it was 'naturally dispersed,' which means it either volatized and people can be exposed to breathing it or it turned into a slick and dispersed over water, ultimately going into the Gulf and in the meantime slicking large areas of wetland and residential areas," said Olson.
The Coast Guard has concentrated on the big spills, but spills in hard-to-reach, hard-hit areas of the coast have not been addressed. "It's rare that you actually recover more than 20 percent of the oil," Olson said.
The long-term effects of the storm -- the damage to natural resources and the Gulf Coast ecosystem -- may not be known for months or maybe years.
Along Louisiana's coastal marshlands, home to a large population of birds and wildlife, scientists say the damage caused by oil and other chemicals could be disastrous.
"Crude is the least of the problem," Dr. Paul Sammarco, a researcher at the Louisiana Universities Marine Consortium, told the Wall Street Journal. Once contained and removed the oil could have little effect, but petrochemicals and other refined products such as diesel fuel could be toxic, according to Sammarco. "They are much more difficult to deal with," he said.
Ongoing assessments conducted by the EPA, the main environmental agency responding to the disaster, and the Coast Guard, showed high levels of bacteria in flood waters and mud in affected neighborhoods in Louisiana early in the response phase, but showed that damage to fisheries along the coast may have been limited.
The agency began conducting daily assessments of drinking water, wastewater, solid waste and soil in the city of New Orleans days after the storm. One assessment, conducted on Sept. 27, showed high levels of petroleum hydrocarbons, or fuel oils, and E. coli bacteria in sediment samples of residue left over from receding floodwaters.
But the long-term environmental impacts of the storm are impossible to predict, according to EPA spokesman Michael Dorff.
"We are not in a position to speculate what the long-term effects are going to be. It's going to take a little bit to pull it all together and get the big picture and figure out what this is going to mean for the future," Dorff said.
In a disaster such as Katrina, according to Dorff, the EPA is responsible for releases of hazardous materials that might be dangerous to human health or the environment, but "at this point, we're still in the assessment phase."
Plans to begin restoring the environment are expected to start with major engineering projects to repair leaks. Workers will begin by removing mass amounts of debris -- estimates have put the amount at 100 million cubic yards or 22 million tons -- repairing water and sewer systems and repairing leaking gas station tanks and leaks from chemical plants, a Dallas Morning News report said.
The cleanup also has become mired in politics.
Environment groups have argued that lawmakers have used hurricanes Katrina and Rita to ease environmental standards on the oil and gas industry.
"This really has very little to do with the hurricanes or relief efforts or even refiners," the NRDC's John Walke told Reuters on Sept. 27 after the House Energy and Commerce Committee and the House Resources Committee met to decide on a plan to relax air standards for coal-fired power plans and expand offshore oil drilling. "This is deregulation pure and simple," he said.
But some lawmakers say easing standards would allow refiners and others to recover and expand following the lost supplies caused by the two hurricanes. Rep. Joe Barton, R-Texas, said tough permitting and emission rules also hurt industries during natural disasters.
"We don't want more emissions but we do want to give existing industrial facilities the ability to retrofit and modernize without going through a laborious permitting process," he told Reuters.
The House passed Barton's bill, the Gasoline for America's Security Act, which would ease emissions standards, but minus a section that would have expanded U.S. drilling, by a 212-210 vote on Oct. 7, 2005. By mid-October, the Senate had yet to vote on the bill.