Swamp tour guide Arthur Matherne stands on the bow of his airboat in the marshes south of the Davis Pond Freshwater Diversion. He believes increasing the flows of Mississippi River water into the Barataria Basin will build more land and help wildlife. (Photo by Tristan Baurick/Verite News)
DES ALLEMANDS — Arthur Matherne is used to speeding his airboat across this stretch of the Louisiana coast, where lakes and bayous have widened as the Gulf of Mexico’s salty water has moved in, dissolving marshes and swamps.
But in one tucked-away patch of the Barataria Basin, the semi-retired tour guide eases off the throttle as he tries to remember his way through channels that have grown tighter by the year. Grasses are overtaking the shallows, and oak branches are spreading overhead, dangling Spanish moss over waterways he once barreled through.
“All this, it’s filling in,” he said after shutting off his boat’s roaring propeller. “Right here, it used to be three feet of water. Now it’s three inches.”
What Matherne is seeing is a striking reversal of a pattern that has defined south Louisiana for the past century. While much of the coastal zone has receded at about 11 square miles per year, the wetlands here are gaining ground.
The reason is just a few miles away. Near Luling in St. Charles Parish, the Davis Pond Freshwater Diversion has funneled Mississippi River water into the basin for 24 years to combat saltwater intrusion. But something unexpected happened. The diversion also carried the muddy river’s sediment into the wetlands, raising the bottom and helping create new land.
“It’s had this unintended consequence of building land,” said Jacob Berkowitz, an Army Corps of Engineers wetland scientist. “This became one of the strategies that’s considered a key to addressing coastal land loss in Louisiana.”
Yet even as Davis Pond demonstrates the land-building potential of river diversions, Louisiana has abandoned its most ambitious attempt to put that approach to work. Last year, the state canceled the massive Mid-Barataria Sediment Diversion, a $3 billion project inspired by Davis Pond and once heralded by the state as “the largest and boldest environmental restoration project in U.S. history.”
Though it broke ground in 2023, work stopped shortly after Gov. Jeff Landry, a Republican and one of the diversion’s most prominent critics, took office in 2024. He officially terminated the project, which would have been located 20 miles south of New Orleans, in July 2025.
Landry called the diversion a costly and ineffective “experiment” that would harm the commercial fishing industry by flooding parts of Barataria Bay with too much freshwater and sediment, pushing out shrimp and burying oysters.
“This project is going to break our culture,” Landry told state lawmakers in 2024. “It will destroy the shrimping industry – which is already struggling – and destroy the oyster beds.”
Also canceled was a companion project – the $1.8 billion Mid-Breton Sediment Diversion, aimed at reviving dying wetlands southeast of New Orleans.
Despite Landry’s opposition to these projects, his administration is quietly planning more diversions along the Mississippi, albeit on a smaller scale and with less fanfare.
Officials with the Louisiana Coastal Protection and Restoration Authority declined to discuss the state’s diversion plans, but a Verite News review of agency budget documents indicates the state plans to spend at least $340 million on five projects over the next several years that would divert Mississippi River water to restore coastal wetlands.
That represents a big increase over past spending on diversions. Since 2007, CPRA has completed just three diversion projects totaling $47 million, according to the agency’s 2027 annual plan.
While some state leaders may disparage diversions, CPRA scientists still believe using river water to rebuild land and restore wetlands is a sound approach. At its core, a diversion mimics how the Mississippi functioned before levees walled off its floodplain, preventing the river from overflowing its banks or breaking through them at points called crevasses, CPRA coastal scientist Brian Gossman said during a public lecture in March.
“The natural process that we’re attempting to harness is the Delta cycle,” he said. “It’s the same process that built all of coastal Louisiana over millennia. We’re just using it in a targeted way.”
About 98% of the CPRA’s planned diversion spending would go to one project — the restoration of Maurepas Swamp, a Chicago-sized wetland along the west edge of Lake Pontchartrain, about 25 miles from New Orleans.
The $334 million project, which broke ground in 2024, will install gates in the Mississippi River levee near Garyville and channel up to 2,000 cubic feet per second of water into Maurepas, which remains one of the country’s largest swamps despite losing thousands of acres of cypress and tupelo forest. Levees built in the early 1900s cut the swamp off from freshwater and sediment, leaving its trees vulnerable to saltwater intrusion.
According to the CPRA, the diversion will rebuild lost land and flush out stagnant, salty water, rejuvenating about 45,000 acres. It’s set for completion late next year.
The CPRA hasn’t totally given up on diverting sediment into the Barataria Basin. After canceling the Mid-Barataria Sediment Diversion, the agency dusted off an earlier, much smaller version of the project: the Medium Diversion at Myrtle Grove. Proposed more than 25 years ago, the project would divert up to 15,000 cubic feet of river water per second into the basin — about one-third of Mid-Barataria’s typical operating rate. The diversion would be supplemented by dredging sediment directly from the Mississippi and placing it in the basin to accelerate marsh building.
The Myrtle Grove project’s timeline and budget are unclear. CPRA budget documents indicate about $1.7 million could be spent on the project between 2027 and 2029, but the full cost will likely be much more. In 2012, the project was estimated at $278 million, or about $480 million in today’s dollars.
CPRA’s spending plans would also boost the Davis Pond diversion. The agency has proposed spending $3 million, shared with the Army Corps, to study how the diversion could be operated to build more land.
Research led by Tulane University in 2019 suggested that boosting the diversion’s average flow from 1,000 to between 4,000 and 7,000 cubic feet per second could deliver more sediment to nearby wetlands. But if the flow is too high, researchers warned, the sediment will be flushed away.
“It is a delicate balance,” wrote Molly Keogh, a coastal geologist who took part in the research. “Water carries sediment, so the more water that is diverted, the more sediment enters the wetland. But if too much water is diverted, the water will be flowing too quickly for the sediment to be deposited in the diversion’s ponding area.”
Finding ways to increase the diversion’s flows has strong support in St. Charles Parish, where Davis Pond is located. In its 2025 habitat restoration plan, the parish endorsed the proposed CPRA study, citing criticism that the diversion’s operations were “not being aggressive enough” to maximize its benefits.
Watching Davis Pond’s silty flows creep past his airboat, Matherne agreed the diversion should release more water and sediment.
“Right now, it’s like pissing in an Olympic-size swimming pool,” he said. “We need more flow.”
Built in 2002 by the Army Corps, the diversion was initially intended to improve oyster beds that had become too salty as coastal marshes receded. Oyster abundance in the area has fluctuated since the diversion was built, but recent monitoring data suggests populations on public beds were above their 10-year averages in 2024, according to Danielle Richardi, a CPRA coastal scientist. Shrimp catches south of the diversion hit a nearly four-decade high that same year, she said.
Matherne said he’s seen a marked increase in wildlife. Alligators are more plentiful, he said, pointing out more than a dozen of the reptiles as his boat traveled the maze of waterways near the diversion.
“All the alligators you see – that’s a fraction of what’s out there,” he said. “Come back at night, and you’ll see their eyes shining all over.”
Several studies have documented sediment accumulation and land building near the diversion, although researchers in recent years have reached conflicting conclusions about the overall impact on wetland acreage.
In 2019, Louisiana State University coastal sciences professor Eugene Turner challenged conventional thinking about river diversions with a study linking Davis Pond to increased wetland loss. Turner found that the annual rate of wetland loss near Davis Pond nearly tripled after the diversion began operating, increasing from 0.36% to more than 1%. The increase was greater than in nearby wetlands unaffected by the diversion.
While the diversion was intended to restore the Mississippi’s pre-levee connections to surrounding wetlands, the river’s water has changed dramatically over the past century. It now carries high concentrations of nitrogen and phosphorus, much of it from fertilizer and manure runoff from farms and wastewater discharged by cities upstream.
Turner argues that the excess nutrients produce wetland plants that are, essentially, flabby and weak.
“If your garden is fertilized too much, it puts all its growth aboveground,” he said. “It falls over because its roots never had to work hard.”
Turner believes that lower nutrient levels encourage plants to develop stronger root systems, making marshes more resistant to erosion.
He likens some of the apparent land gains from diversions to a “green toupee.” The wetlands may look as though they’re filling in, but strong winds or currents can easily strip away the vegetation.
Two of Turner’s colleagues disputed his findings in a 2023 study. John White and John Day, also LSU coastal sciences professors, found that the first 20 years of Davis Pond’s operations had actually led to a net gain of 1.3 square miles of land. Their study said Turner came to an “erroneous conclusion” by incorrectly using data “that was clearly labeled as inappropriate for the task.”
The researchers asserted that Turner’s satellite data were too imprecise to distinguish small patches of wetlands from open water, potentially making land appear to have disappeared when it hadn’t.
Turner stands by his findings, arguing they more accurately portray how diversions affect coastal wetlands and warn of the damage they can cause if poorly managed.
Opponents of the Mid-Barataria diversion regularly cited Turner’s research and added several more concerns, including the CPRA’s projections that the huge diversion could bury oyster beds under sediment and that added freshwater would likely push shrimp farther offshore, making them harder to catch. Combined with the project’s $3 billion price tag, those concerns cratered political support.
“Considering the uncertainties and questionable environmental outcomes recognized by various agencies … it was necessary to abandon the current project,” CPRA Chairman Gordon Dove wrote in a column.
Although the CPRA has yet to fully explain its new approach to diversions, smaller and cheaper projects appear to be a priority. Turner welcomes that shift, but argues diversions should also operate at lower flows to avoid washing away vegetation that he believes excessive nutrients have weakened. He also recommends building diversions in areas with sandy soils rather than the soft, unstable soil in many marshes.
“It’s not that they won’t work,” he said. “These diversions give you lessons. We should learn from them.”
This article first appeared on Verite News New Orleans and is republished here under a Creative Commons Attribution-NoDerivatives 4.0 International License.
