As politicians argue over just how much land the Mid-Barataria Sediment Diversion could build along a rapidly sinking coast, geologist Alex Kolker regularly makes the 65-mile drive down from New Orleans to document Neptune Pass, the largest new branch of the Mississippi River to form in nearly a century.

As the fast-flowing river water carries sediment into the Neptune Pass channel, the water slows down just enough to drop silt, sand and clay in the bay. Kolker, an associate professor at the Louisiana Universities Marine Consortium, has stood knee-deep in the new land that’s visible during periods of low flow near where Neptune Pass splits the east bank of the Mississippi River, across from the small fishing town of Buras, Louisiana. 

Such splits are not unheard of. Locals refer to a natural break in the riverbank as a “crevasse.” But Neptune Pass likely started as a navigational cut made by a petrochemical company. Then, in 2019, flooding pushed the narrow channel into a widening crevasse. 

To mirror what Neptune Pass is doing on its own, state scientists spent nearly two decades designing a man-made structure, using research that dates back 40 years. The structure, called the Mid-Barataria Sediment Diversion project, is to be located on the west side of the Mississippi River about 35 miles upriver from Neptune Pass, near the small town of Myrtle Grove.

The $3 billion Mid-Barataria project, which broke ground in 2023, was seen as the ambitious lynchpin of the Louisiana Coastal Master Plan. “Today will be remembered as a critical turning point for Louisiana’s coast,” said then-Gov. John Bel Edwards at the groundbreaking.

The project had been envisioned since 2007 within the Coastal Master Plan, which called for the construction of a sediment diversion that would deliver fresh water and land-building alluvium to Barataria Bay, an area of eroding wetlands west of the Mississippi River that was severely damaged by the 2010 Deepwater Horizon Oil Spill. 

Now entangled in politics, the coastal restoration project has stalled. 

But downriver, the Neptune Pass is thriving. What began in 2019 as a thin channel has since widened and deepened enough that its water volume now ranks as the 10th largest river in North America, or the 100th largest river on Earth. 

During periods of high flow, Neptune Pass carries about 15-17% of the flow of the Mississippi, according to new research led by Kolker.

By design, the Mid-Barataria Sediment Diversion would carry less of the Mississippi River’s flow than Neptune Pass, about half the volume of the growing crevasse. But it may never become operational. On the heels of new scrutiny about how much land the project can actually build, officials have indefinitely delayed its construction.

Gov. Jeff Landry, who had been critical of the project before he took office, prompted a review of previously conducted research, which included a 2022 modeling study that he said was omitted from a permit application with the U.S. Army Corps of Engineers. The modeling study, prepared by engineering and environmental consultant FTN Associates, concluded that the diversion might create only a third of the land officially predicted at the groundbreaking. 

The newly surfaced 2022 study estimated that the project could build as few as seven square miles of wetlands—far less than estimated by the primary model, which was submitted as part of the Army Corps’ exhaustive environmental study and concluded that the diversion could build 21 square miles of lost wetlands over 50 years.

In mid-April, before the modeling controversy was made public, the Louisiana Coastal Restoration and Protection Authority (CPRA) voted to fully fund its nearly $2 billion spending plan for the next fiscal year, which hinges on the Mid-Barataria Sediment Diversion project.

On April 25, the Army Corps suspended a key permit to build the massive coastal restoration project, which was already under a 90-day work pause issued by Landry.

“This suspension is based on the state’s actions, including failures to act or to obtain compromise, its public statements and positions, the new information and potentially changed circumstances since permit issuance,” Army Corps Col. Cullen Jones wrote in a letter to CPRA Chairman Gordon Dove. The six reasons for suspension also included the state’s assertion that it would not be able to afford the dredging required by the diversion and the lack of an agreement between the state and Plaquemines Parish officials about compliance with the National Flood Insurance Program requirements, given “the increased water levels to be caused by operation of the Mid-Barataria diversion.” 

In an earlier email, dated March 31, Jones had written that the permit would not be affected following a technical review of the 2022 modeling study. 

Ultimately, the Army Corps said the state “deliberately withheld information” from the Corps’ environmental review. That new information had changed the “balance of benefits versus harms,” Jones wrote.

Then discussions about the review shifted from land-building estimates to mud-slinging. 

Last Monday, Landry accused the Bel Edwards administration of hiding the unfavorable modeling report from the public and the Army Corps. 

“Turns out they only ‘trust science’ when it’s convenient to their narrative,” Landry wrote on X, linking to reporting from the Associated Press. 

Bel Edwards denies that his administration withheld information during the permit application process. The 2022 model – and its shortcomings – were shared and discussed with the National Oceanic and Atmospheric Administration (NOAA), the lead federal agency for the project, and the Army Corps, Bel Edwards contended, in a May 6 letter to Col. Jones.

As had been discussed, Bel Edwards wrote, the FTN modeling omitted several important considerations for land building, such as sea level rise, he said, and mischaracterized the potential annual cost of dredging for the diversion channel, sediment that would ultimately contribute to new wetlands.

“Even the worst-case scenarios in the FTN model found that the need for dredging only occurs in later years of operation, not annually and very little during the first 30 years of operation,” Bel Edwards wrote.

What Stands to Be Lost

On a clear April day, Captain Ryan Lambert launched his boat from a dock in Buras, near Cajun Fishing Adventures, a business he founded in 1980 as a family-oriented charter boat fishing and duck-hunting operation. 

Lambert aimed his boat across the Mississippi to the river’s east bank and entered Neptune Pass, the channel that has rapidly expanded since the Mississippi River floods in 2019. Often, he is transporting fishermen hoping to reel in sport fish. But on this day, Lambert was transporting coastal scientists to Quarantine Bay to research the fast-growing delta in Louisiana.

Scientists along the Gulf Coast haven’t seen anything like it for half a century, not since the emergence of the Wax Lake Delta about 150 miles west in the 1970s.

Lambert, born and raised in South Louisiana, told the scientists what indicators he looks for to determine if fishing grounds are in good health. He pointed to aquatic vegetation popping up in Bay Denesse. “That’s nature’s filter,” he said. “All of the juvenile fish, crab and shrimp will be raised in that grass to save it from predation.”

On the other side of the river, in the Barataria Basin where Louisiana sited the Mid-Barataria Sediment Diversion project, there’s no such vibrancy. “The estuary is literally eating itself,” he said. “It’s a dead zone on the other side. The only thing we have there is oysters now.”

To properly nurture native sea creatures, these brackish wetlands must stay slightly salty, but not too salty.

That balance has been disturbed for more than a century by manmade structures. The levees built to block floodwaters from people’s homes have kept fresh water from reaching wetlands. In the wetlands of Barataria Basin, the aquatic vegetation has been starved of necessary river water and sediment. Paths cut through marshes by petroleum companies hastened the intrusion of salt water into wetlands along the Gulf Coast, killing important plant life. 

Today, the open, salty water is a prime location for oyster farmers, who sued the Army Corps, the U.S. National Marine Fisheries Service and the U.S. Fish and Wildlife Service in 2024 to halt construction on the controversial coastal restoration project, fearing that any influx of fresh water would harm the conditions for oyster hatchery production.

The Mid-Barataria Sediment Diversion project would funnel hundreds of thousands of cubic feet per second of fresh water into the salty oyster fishery in West Plaquemines Parish. The oyster farmers and some conservationists argue that pollution from the river water would wipe out the oyster fishery and impact at least three species of endangered sea turtles, as well as endangered birds such as the red knot and piping plover. 

Still, the diversion’s Mid-Barataria location was researched over decades to find the most cost-effective place to build the largest area of land, according to Restore the Mississippi River Delta, a nonprofit coalition of environmentalists. 

Earlier this year, the coalition contracted Global Strategy Group to poll Louisiana voters on their support for large coastal restoration projects such as the Mid-Barataria. They found bipartisan support for action to address the state’s land loss crisis, with 73% of voters supporting sediment diversions, up from 68% in 2021.

“Sediment diversions are the best and most sustainable solution to protect Louisiana’s communities from storm surges and coastal flooding and help make living in the state less expensive,” said Simone Maloz, campaign director of Restore the Mississippi River Delta. “Voters understand these diversions are an essential component of our restoration plans,” she said.

Without intervention, Plaquemines Parish is at risk of disappearing, Lambert warns. The diversion might harm the oyster industry, he said, but until the flow of fresh water and sediment is restored to the Barataria Basin, “everything’s gonna die and we’re gonna sink into the abyss and we can’t live here anymore.”

What is Growing

After years of relatively low Mississippi River flow, a recent flood stage threatened to crest at a level that could trigger the Army Corps to open the Bonnet Carré Spillway, which opens up a side of the river, diverting river water into Lake Pontchartrain and reducing pressure on downriver levees. The Bonnet Carré was last opened in 2020.

But the crest has waned, leading the Army Corps to announce that it doesn’t expect to open the spillway.

Yet the water is still high enough to deliver large amounts of sediment to Louisiana from the river’s enormous drainage basin, consisting of 41% of the continental U.S. Much of the sediment is expected to show up at the end of Neptune Pass, further building up wetlands in Quarantine and Bay Denesse.

“In the past these high river flows have been major land-building events,”  said Alisha Renfro, senior manager for Science Policy for the National Wildlife Federation’s Gulf of Mexico Program, who recalled the land built in the Wax Lake delta after the 1973 flood and by the West Bay Sediment Diversion after the 2011 flood. “Once the floodwaters dropped, new land was revealed, and we are likely to see that this year in Quarantine Bay,” she said.

Renfro worked with Kolker on recent research to calculate how much of Quarantine Bay’s new land came from sediment collected by the Mississippi River along its 2,340-mile route, versus sediment eroded from the banks of the growing crevasse.

Using sediment-core collections from Quarantine Bay and other data, the team found that the new delta is 56-79% larger than the material excavated from Neptune Pass. Between 2019 and 2022, they found, six million cubic yards of sediment were diverted from the Mississippi through Neptune Pass and deposited into Quarantine and Bay Denesse.

“Our research shows that Neptune Pass is building land in a manner that follows the basic principles of delta geology. These same geological principles also underlie the diversions that are part of Louisiana’s Coastal Master Plan,” Kolker said.

Keeping Cargo Moving on the River

The Mississippi River is designed as a self-scouring channel, with the water flowing at a rate high enough to kick sediment out into the Gulf of Mexico and away from Louisiana’s starving wetlands. But as the Mississippi River loses water to Neptune Pass, the river becomes shallower, creating shipping hazards. That left the Army Corps to weigh the benefits of Neptune Pass creating new land along a rapidly sinking coast versus the drawback of lower water on the main Mississippi River channel, which presents navigational hazards for cargo ships.

In 2022, the Army Corps partially stabilized Neptune Pass to reduce shoaling – unexpected shallow areas – in the main river.  Now, the Army Corps has proposed reducing the flow into Neptune Pass to eliminate navigational hazards for ships along the Mississippi River. 

A recent environmental assessment found that building a stone flow-control structure at the Neptune Pass inlet – where it branches from the river – would not significantly affect the human environment. Construction is anticipated to start in the early summer of 2025.

At the outlet, where the channel meets Quarantine and Bay Denesse, the Army Corps will build sediment retention enhancement devices out of stone, dredged material, geotextiles and wooden piles. This technique was shown to induce land building in West Bay, where a sediment diversion project has restored an estimated 9,831 acres of wetlands south of Venice, Louisiana since its completion in 2003.

It’s a balancing act, said Kolker. “I think we would all prefer a Louisiana with more land instead of less, but no one wants to see a barge run aground.”