Over the grand sweep of time, sediments carried down from continents by mighty rivers like the Mississippi have built vast deltas of land and marsh along coastlines. But for a century the U.S. Army Corps of Engineers has built levees along the Mississippi, which have prevented the land-creating sediment in the muddy water from spreading across the delta, starving wetlands of nutrients and raw material. That’s why Louisiana’s 2012 Coastal Master Plan to rebuild the state’s vanishing coastal wetlands relies on cutting gaps in the levees, diverting water and sediment so that the land-building material flows again across parts of the landscape.

The lack of sediments isn’t the only cause of the dramatic loss of wetlands, however. It may not even be the major one, some scientists and legal experts argue. The other culprit: the cutting and dredging of thousands of kilometers of canals by oil, gas and pipeline companies. These canals allow boats, drilling rigs, pipelines and other equipment to get through the marsh, but also permit saltwater to flow into the wetlands, weakening and killing the plants that hold the marsh together. Storms then wash the remaining soil away. “You can make the case that the flood protection levees were not the cause of the wetland loss,” says Gene Turner, professor of oceanography and wetlands studies at Louisiana State University. “Instead, it is the local cuts and nicks, one acre at a time.”

Now, the Southeast Louisiana Flood Protection Authority–East, an independent board set up after Hurricane Katrina to manage flood control for areas in and around New Orleans, is making that case—in court. In July the panel filed suit against 97 energy companies (including BP, Chevron, ConocoPhillips, ExxonMobil, Koch Industries and Shell) for causing the loss of thousands of hectares of wetlands that are vital for protecting the city from storms. Chevron has since asked that the case be moved from state court to U.S. District Court, where the oil company expects a more favorable outcome, with a ruling on the request expected by the end of the year.

According to the lawsuit: “Oil and gas activities continue to transform what was once a stable ecosystem of naturally occurring bayous, small canals and ditches into an extensive—and expanding—network of large and deep canals that continues to widen due to [the] defendants' ongoing failure to maintain this network or restore the ecosystem to its natural state.” The suit asks for billions of dollars in damages.

The lawsuit faces powerful opponents in addition to the oil and gas industry. Gov. Bobby Jindal is against it. So is Garret Graves, Jindal’s appointed director of the state’s Coastal Protection and Restoration Authority, which oversees the plans for sediment diversions. Already Jindal has replaced three members of the nine-person flood control board, which had voted unanimously to pursue the lawsuit. The governor has made it clear that board members who support the suit will not be reappointed when their terms expire.

But the scientific evidence behind the lawsuit is strong, says Oliver Houck, professor of law at Tulane University Law School. Houck points out that the loss of wetlands didn’t start until the oil and gas companies began cutting canals, even though sediment-blocking levees have been in place for more than 100 years. “The damage coincides with the oil and gas industry activities, not the levees,” Houck says. He adds core samples taken in wetlands show that huge swaths of marsh aren’t actually solid land built from sediment. Instead they are made up of masses of plants and organic material, as much as five meters thick, which have built up over many decades.

Some small-scale restoration efforts show that it’s possible to harness this natural plant growth to bring the marsh back—without adding more sediment from the Mississippi River. The trick is to dump the spoil banks (the material originally dredged from the canals and piled on the banks) back into the now abandoned canals. That slows the intrusion of saltwater and helps restore the natural flow of fresher water across the marsh. That, in turn, enables plants to grow, slowly filling the gap “like a wound healing,” Houck says. The process is gradual, taking as much as 20 years. “But the few examples we have of filling these canals show that it works,” Turner says. It’s been done successfully in the Barataria Preserve—a wetland area just south of New Orleans, for instance.

Obviously, the task is more challenging when the spoil banks have already eroded away, too. But in those cases, “the filling can be done from maintenance dredging on the main channels,” Houck explains. “The question is not feasibility, but cost. And the industry that built these canals, profited enormously from them, and caused these losses ought to pay.”