In The Mississippi River Delta - Service canals dug to tap oil and natural gas dart everywhere through the black mangrove shrubs, bird rushes and golden marsh. From the air, they look like a Pac-Man maze superimposed on an estuarine landscape 10 times the size of Grand Canyon National Park.

There are 10,000 miles of these oil canals. They fed America's thirst for energy, but helped bring its biggest delta to the brink of collapse. They also connect an overlooked set of dots in the Hurricane Katrina aftermath: The role that some say the oil industry played in the $135 billion disaster, the nation's costliest.

The delta, formed by the accumulation of the Mississippi River's upstream mud over thousands of years, is a shadow of what it was 100 years ago. Since the 1930s, a fifth of the 10,000-square-mile delta has turned into open water, decreasing the delta's economic and ecologic value by as much as $15 billion a year, according to Louisiana State University studies.

The rate of land loss, among the highest in the world, has exposed New Orleans and hundreds of other communities to the danger of drowning. Katrina made that painfully clear.

"I remember when I was a young boy we had a camp out in the marsh," said Don Griffin, a grocer and seafood dealer in the delta town of Leeville, which became an oil-drilling center for decades. "The same places you used to have to get around with a pirogue and a push pole now you can go with a 25-foot outboard. There's no more marsh, which is your first barrier of defense for hurricanes."

In Katrina's wake, the Army Corps of Engineers has gotten the brunt of the criticism for the disaster. Besides building suspect levees, the Corps' mission to control waterways with spillways, floodgates and other measures has played havoc with nature by restricting the Mississippi's sediment and fresh upriver water from replenishing the delta's wetlands.

There are other reasons for the disastrous wetlands loss: Human development, cypress logging, ill-advised farming on the coast, hurricanes, slipping-and-sliding geologic faults and even a South American semi-aquatic rodent called nutria imported to Louisiana in the 1930s.

But many scientists say the oil industry's 10,000 miles of canals - enough to stretch nearly halfway around the world - and the drilling they supported played a decisive role. Some scientists say drilling caused half of the land loss, or about 1,000 square miles.

"The whole thing was manifest destiny written large on a marshy landscape," said John Day, an LSU professor emeritus who specializes in delta ecologies.

The industry denies that and points to disagreement among scientists over who or what caused damage, and how much.

"I've got duck leases out there and I remember when they were covered in grass. They're all ponds now," said Don Briggs, president of the Louisiana Oil & Gas Association. "It's not gone because of drilling. It's because nutria ate all the grasses."

However, a substantial body of evidence points to oil's heavy toll.

The canals, most dug to access wells by bucket dredges between the 1930s and 1970s when restrictions and mitigation requirements were lax to nonexistent, crisscross the marshy coast like a liquid maze.

In many places, they run perpendicular to the Gulf of Mexico shoreline, allowing salt water to intrude far inland. One spot is dubbed "The Wheel" because a series of canals looks like a wagon wheel from the air.

The muddy slop dredged from the canals had to go somewhere. Oil companies piled it where they found it, creating an estimated 13,000 miles of tide-blocking spoil banks.

R. Eugene Turner, an LSU oceanographer, has calculated that every square mile of the delta is bounded on three sides by oil-canal ridges. Turner has spent more than 30 years studying the oil industry's footprint on the delta.

"If the water is blocked from going in, the wetlands on other side is drier for a little longer and also stays flooded longer than it otherwise would be," Turner said. "By drying it, the land oxidizes and dries out; and if it's wetter, it's like leaving a lawn sprinkler on and the plants are going to die."

The damage doesn't stop with the canals. For example, U.S. Geological Survey scientists say the sucking out of the ground of so much oil and gas likely caused the land in many places to sink by half an inch a year. In oil's heyday 30 years ago, Louisiana's coastal wells pumped 360 million barrels a year, an eighth of what Saudi Arabia ships to the market today.

Oil wells also discharged about a billion gallons daily of brine, thick with naturally occurring subsurface chemicals like chlorides, calcium and magnesium, as well as acids used in drilling.

"It was poured into the marshes," said Virginia Burkett, a longtime researcher of the Louisiana wetlands and the chief scientist for climate change at USGS. It contaminated soils and killed plants and animals, she said, before brine dumping was finally regulated in coastal marshes in 1985.

Still, when politicians in Washington or Louisiana talk about Katrina guilt they blame the Corps of Engineers, global warming and the French for building a city in low-lying swamps nearly 300 years ago - but not the oil industry.

"It's the elephant at the dinner table and nobody wants to say there's an elephant there," said Luke Fontana, a New Orleans lawyer for Save Our Wetlands, one of the state's oldest grassroots environmental groups that has fought the draining of swamps and oil company activity since the 1970s.

But the industry's legacy is getting new attention. Some contrast record petroleum profits with staggering cost estimates - up to $60 billion - to save New Orleans and restore the delta. In 2006, major U.S. oil companies, some of which moved offices from New Orleans to Houston, earned about $162 billion.

Meanwhile, locals increasingly ask why oil shouldn't be made to clean up its profitable mess the same as mining operations had to do in Appalachia.

Delta folks like Griffin, the grocer in Leeville, wonder why Shell, ExxonMobil and other oil behemoths aren't paying for the disappearance of his boyhood duck ponds and dune-lined islands.

"It seems that the government should hold them accountable for some of the problem," Griffin said from behind his cash register.

At mid-20th century, marsh-borne oil derricks towered over Leeville's shacks as far as the eye could see, replacing fields of cotton. Today, those same places, chopped up by bucket dredges, are open water. A town cemetery lies in the water, its tombs barely visible. And as Leeville goes under, New Orleans, 50 miles to the northeast, becomes that much more exposed.

The oil industry has not gone entirely unchallenged.

As far back as the 1970s, landowners and environmental groups were able to stop specific projects or force companies to clean up isolated sites. But no lawsuit or state law has compelled the industry to fill the canals or dismantle old spoil banks.

After Katrina, a class-action lawsuit blamed oil and pipeline companies for "depriving ... New Orleans from its natural protection against hurricane winds and storm surges." The suit was dismissed last October.

In the early 1980s, then-Gov. David Treen proposed a coast-and-levee tax by slapping a levy of 36 cents on every barrel of oil and 6 cents on every 1,000 cubic feet of gas that crossed the coastal plain; but the measure didn't muster the two-thirds majority needed in the state Legislature.

"Today, I would recommend going to two bucks a barrel," Treen said. "That would give us about $1 billion a year. I just feel like they ought to pay for some of the cost we incur."

Eventually, petrodollars may provide relief. In 2006, Congress approved a plan to give Louisiana and other Gulf states a large portion of offshore royalties the industry now pays to the federal Treasury. By 2017, Louisiana hopes to get as much as $650 million a year.

Meanwhile, the anything-goes days for oil are over. Regulators demand the use of less-damaging techniques - directional drilling, rerouting of pipelines, wetlands mitigation. Private landowners often ask oil companies to clean up after themselves.

"My job is to make sure they stay on their right of ways, that they don't traverse onto vegetative areas or use machinery that is harmful," said Forrest Travirca III, a land warden for a swath of wetlands near Leeville held by a public trust.

"It's like strip mining. A good strip miner will repair the land."

Cruising in his bay boat through mangrove brakes and past tugboats and crew vessels docked at the offshore-drilling port of Port Fourchon, Travirca pointed out places where oil companies have patched up the land.

For its part, the industry balks at talk of paying for the damage.

"Worldwide, there's this notion that they want the oil industry to pay for everything," John Felmy, chief economist of the American Petroleum Institute, said during the organization's recent meeting in New Orleans. "It's like the world considers the industry a cookie jar."

The industry denies that drilling damaged the delta that much.

"The real question is, what damage did occur?" said Jim Porter, president of Louisiana's chief oil lobby, the Louisiana Mid-Continent Oil and Gas Association. "There's no clear-cut answer on it. But there is no doubt there are many, many causes for wetlands loss and access to oil and gas operations is rather insignificant."

In the 1980s, Porter was in charge of the Louisiana Department of Natural Resources, the agency that regulates drilling and coastal conservation.

Rex Tillerson, chief executive of ExxonMobil Corp., said at the American Petroleum Institute meeting that there were "a lot of reasons" for the delta's decline, including the unstable geology there. "The land moves around a lot along the coast," he said. Geologists say there is evidence that slipping-and-sliding faults have caused land loss.

For now, the oil companies are winning the public relations battle, in part by spending $5 million on a marketing campaign called America's Wetland. "Tell Washington to shore up America's energy coast. It fuels the nation," one TV ad implores, calling on Congress to spend the money it will take to restore the delta. Nowhere is oil's responsibility mentioned.

Many Louisiana politicians, including former Gov. Kathleen Blanco, have backed the campaign.

Taking the other side is a disparate group - among them, Treen; Tab Benoit, a Cajun rock musician who talks about oil's legacy during national tours; and Walter Williams, a writer and animator known for his clay-figure character Mr. Bill, who blogs about it.

"Cigarettes were an easy whipping boy," said Williams. "Oil permeates."

In fact, the industry is resurgent in the delta where, as oil prices soar, wildcatters are turning on long-dormant wells.