Since the 1930s, Louisiana has lost roughly as much land as makes up the state of Delaware.

"If you put the state of Delaware between New Orleans and the ocean, we wouldn't need any levees at all," says John Barry, vice president of the Southeast Louisiana Flood Protection Authority-East. "There is this large buffer of land that has disappeared, and that buffer makes New Orleans much more vulnerable to hurricanes."

Barry's board has the job of maintaining and improving the levee system that the federal government fortified after Hurricane Katrina pummeled the city in 2005. He says it will be so expensive to keep the city safe that his board decided to try to get money from the oil and gas industry to help do that.

On Wednesday, the board sued the industry, arguing that it is responsible for a big part of the problem, and hasn't paid its fair share to protect the city.

Barry says the industry contributed to the problem in a couple of ways: By sucking the oil and gas out of the ground, it caused the land to sink. The industry has also dug thousands of miles of channels to lay pipeline and reach well sites, which allows saltwater to seep in to swamps and marshes.

That process "kills the plant life, and without the root system, the land basically melts into the ocean," Barry says.

U.S. Geological Survey scientist Jeff Williams worked on a study published in 2000 that found the industry was responsible for more than a third of the wetland losses. "The scientific evidence is very strong," he says.

Williams says he's not surprised that the flood protection board is suing. "What surprises me is that it hasn't happened decades ago."

Other scientists say it's impossible to figure out what portion of the problem was caused by the industry. There are so many natural and man-made causes.

For hundreds of years, the Mississippi River was re-engineered to benefit navigation and farmers. That has prevented the sediment from the river from rebuilding the land in the Louisiana Delta. The land in southern Louisiana is naturally subsiding, and the sea level is rising due to climate change.

Don Briggs, the president of the Louisiana Oil and Gas Association, represents many of the 97 companies named in the lawsuit. He says it's wrong to blame the industry.

"There are many factors. And the biggest factor of all is the fact that we diverted the Mississippi River and the flow of the sediment that created the barrier islands, which gave us the protection that we needed," he says. "The oil and gas industry didn't do that."

Besides, Briggs says that many millions of dollars of royalty money from the oil and gas companies flow to Louisiana every year to restore the coastal wetlands.

"The industry is paying, and does pay," he says.

But legal experts say the companies pay nothing beyond the royalties they have to pay the government for using the natural resources that belong to everyone.

Tulane University Law School research fellow Mark Davis says that for decades, Louisiana politicians have been unwilling to make the industry pay for its damages because of the economic benefits it brings the state.

"I think what we're seeing now is at least one part of the state is saying, 'We're making that demand now,' " Davis says.

But Louisiana Gov. Bobby Jindal, who appointed the flood protection board, has a different demand: He ordered the board to drop its lawsuit and fire its lawyers.

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