Covering a million acres along Louisiana’s central southwest coast, the Atchafalaya Basin is the largest contiguous swamp in North America. It’s home to centuries-old tupelo and cypress trees, along with dozens of species of shellfish and fish, from shrimp and crawfish to freshwater drum and catfish.

This abundance makes the Basin one the most important points on the Mississippi Flyway, a bustling migratory route that millions of birds travel annually, stretching from breeding grounds in Canada to wintering grounds in Central and South America.

Herons, egrets, ibis, spoonbills, and more than three hundred other species — about 60 percent of all North American migratory birds — pass through the Basin.

The Atchafalaya is also one of the last places in Louisiana where people still make a living off the land, says Dean Wilson, executive director and founder of the conservation group Atchafalaya Basinkeeper. “It’s the last bastion of the Cajun culture, which is based on seafood and sunlight,” he said. But after decades of development that has changed the ecosystem, he fears it won’t be for much longer.

“Basically it’s only crawfish that’s left, the last of the seafood industries,” said Wilson. “All the others are gone.”

For more than a century, oil companies have drilled, laid pipelines, and cut channels throughout the Basin. The region is littered with discarded stacks of valves, networks of rusted pipes, and abandoned two-story tall steel tanks. These so-called “orphan wells” can leak oilfield waste and cancer-causing chemicals, such as benzene, into the environment.

But environmental advocates say the biggest threat to the Atchafalaya Basin’s fragile ecological balance are river diversion projects.

Supporters of these projects say they benefit the Atchafalaya by improving water quality. But others point to projects of decades past that, by altering the flow of the Atchafalaya River, have dumped tons of sand and silt as well as nitrogen-laden agricultural runoff into the Basin, filling in waterways and suffocating aquatic life.

Louisiana’s Coastal Protection and Restoration Authority (CPRA) is currently seeking permits to begin construction of the East Grand Lake project, a component of the larger Atchafalaya Basin Program. In the works since 2010, the East Grand Lake project would make cuts in elevated banks and spoil piles — 10-foot-tall piles of topsoil, excavated during the construction of pipelines and oil wells, that block the natural flow of water. The cuts would introduce river water into more than 72,000 acres of back swamps on the east side of the Atchafalaya Basin.

CPRA has applied to the U.S. Army Corps of Engineers for a permit to begin dredging and filling wetlands for the project, and to the Louisiana Department of Environmental Quality (LDEQ) for a water quality certification.

The project is projected to cost $3.5 million and take two years to complete.

Louisiana’s Department of Natural Resources has said that the project addresses problems created by the oil industry’s decades of “existing production infrastructure” in the Basin, which have “altered water flow and sediment distribution patterns and continue to cause problems for water movement.” The agency contends that by realigning water flow patterns and redirecting sediment, the East Grand Lake project will improve water quality and wildlife habitat.

Shell Oil, which has legacy oil well sites and out-of-compliance canals throughout the Basin, has backed the project. In 2015 the company donated $1.6 million to The Nature Conservancy, which has long supported East Grand Lake, to help fund purchases of privately-owned land within the project’s projected boundaries.

The Nature Conservancy considers the project vital to improving water flow through the swamp, and has worked with large landowners in the Basin, like Wilbert’s Sons, which uses its land for drilling oil and gas wells and laying pipelines as well as harvesting timber.

The group has also partnered with area pipeline companies to raise over $2.8 million to help fund East Grand Lake. They include Enterprise Products, a large supplier of pipeline construction equipment in the area, and Caterpillar Foundation, one of the Basin’s biggest pipeline companies.

The Nature Conservancy, Shell Oil, Enterprise Products, and Caterpillar Foundation did not respond to requests for comment.

Republican Rep. Garret Graves, whose 6th congressional district encompasses the Atchafalaya Basin, is also an East Grand Lake supporter. Prior to his first run for office in 2014, Graves was the chair of the CPRA.

For locals who live, work, and recreate in the Basin, East Grand Lake is just the latest in a long line of projects that have failed to deliver what they promised.

“I’ve been seeing the ramifications of what has been done over the years,” said Jody Meche, president of the Louisiana Crawfish Producers Association-West, which opposes the project. “You know, as a fisherman, you got to pay attention to your environment, you rely on good current flow, you rely on good conditions to make your living.”

Rather than improving fisheries with an influx of fresh water, he said, past water diversion projects such as the controversial Buffalo Cove Water Management project, instead delivered enough sediment to fill in thousands of acres of back swamps until they were no longer navigable by boat.

Meche, Wilson and others contend that filling in the swamps is a big motivation behind oil and pipeline company support for East Grand Lake, because it creates additional land for drilling and pipeline leases. Their groups have joined forces with others, including the Waterkeepers Alliance, Healthy Gulf, and the local Delta Chapter of the Sierra Club, to try and get regulators to halt East Grand Lake.

“We have asked [the Louisiana Department of Environmental Quality] to deny CPRA’s application for a water quality certification because the EGL project will cause or contribute to a violation of state water quality standards,” said Lisa Jordan, an attorney with the Tulane Environmental Law Clinic, which is representing the groups.

Jordan said that the project would violate state standards for turbidity, total suspended solids, and nutrients in the Basin. It would also contribute to further depletion of dissolved oxygen in the swamp, she said, which is already so low that it is impairing fish and wildlife reproduction.

At the federal level, the groups are asking the Army Corps to conduct a more comprehensive environmental impact assessment of the project than currently planned, said Jordan, or simply deny the project a permit. They are also petitioning the EPA to ask the Army Corps for a more comprehensive impact analysis.

In December, Meche and other opponents of the project spoke out during a public hearing about East Grand Lake at the Iberville Parish courthouse in Plaquemine.

“The more we find out about this project, we know it’s going to be a breaking of something that was made by God,” said Russel Honoré, leader of the GreenARMY, an alliance of civic, community, and environmental groups and concerned residents from across Louisiana.

As an Army lieutenant general, Honorė commanded military relief efforts along the Gulf Coast in the wake of 2005’s Hurricane Katrina.

Honoré pointed to previous state-supported projects which, he said, ended up benefitting oil and gas companies and damaging the Basin’s ecosystem, among them the 1959 Florida Gas Transmission pipeline.

“Permits are nothing more than a permit to pollute or to disrupt the natural lay of the land,” Honoré said.

“We will have no future if we keep filling up the Basin,” Atchafalaya Basinkeeper’s Wilson said during the hearing. “We are sacrificing the future of our kids and grandkids to live in the community that we love so much.”

A CPRA public information officer who attended the meeting, Nick Gremillion, did not appear to take notes and declined an invitation to speak.

Joe Baustian, a wetland ecologist at The Nature Conservancy, said at the hearing that the project was aligned with the group’s mission “to protect all protected lands and waters in which all life depends.”

Baustian said that East Grand Lake would improve local water quality by increasing dissolved oxygen concentrations, as well as lowering nitrogen levels contributing to oxygen depletion. He also downplayed the scale of the project. “It’s a small project by intention,” he said. “It’s sort of a proof of concept to see if this type of project can work.”

Other conservationists working in the area disagree. “The idea that this is an experimental project is absurd,” said Woody Martin, a member of the Delta Chapter of the Sierra Club, “because we’ve done this numerous times.”

Martin pointed to the Buffalo Cove project, which the Army Corps described as “designed to improve water circulation and sediment management…in an effort to enhance fish and wildlife resources.” According to Martin, the project flooded the swamp with sediment and fertilizer from the 33 states in the Mississippi River Basin, and devastated the Atachafalaya’s once-pristine expanse of clear, black-green water.

“We already know what’s going to happen if they do the project,” Martin said. “So the better alternative in some cases, and in this case, is not to do the project.”