On Tuesday, the state’s Coastal Protection and Restoration Authority (CPRA) officially began to reconnect the Mississippi River with the Maurepas Swamp, a degraded and submerged swamp forest directly west of Lake Pontchartrain. 

Levees built to protect greater New Orleans had cut off the Maurepas Swamp from the fresh water supplied by the Mississippi River and the Pontchartrain Basin, starving the swamp of nutrients, oxygen and sediment. 

Now, the CPRA is poised to reintroduce the river to the dying swamp through a new channel that runs from the river to the swamp, ending just north of Interstate 10. The flow of water coming into the swamp will be controlled by a gate across the channel at Garyville. 

The new channel is remarkable because it will be the first large diversion carrying river water to a submerging freshwater swamp forest. The project also showcases a new partnership between the U.S. Army Corps of Engineers and CPRA to jolt Maurepas back to life even as the Corps builds new River Parish levees, which will create further separation between the swamp and river.

To a layperson driving down I-10, the Maurepas Swamp seems green and woody – and may not look like it’s dying. At 220 square miles, it’s still considered one of the Gulf Coast’s largest forested wetlands. But without fresh water, the forested area of the swamp is disappearing. 

“This is a swamp that’s been cut off from fresh water and nutrients from the Mississippi River for more than 100 years,” said Alisha Renfro, senior scientist at the National Wildlife Federation. “So it’s been dying for a really long time.”

Most of the river’s levees were built up during the 1920s and 1930s, after record-breaking floods prompted the passage of federal flood-control acts.  

“The swamp is still here – there are still trees – they are just really unhealthy,” said Brad Miller, CPRA project manager for the river reintroduction. Tuesday’s groundbreaking marked the beginning of construction for the freshwater diversion, which should be completed by 2028. Imagining the complex project took nearly 10 times as long: its planning and design phases lasted almost 30 years.

The devastated health of the cypress-tupelo forest is best seen from the swamp’s interior. In a healthy swamp forest, the canopy would be closed, with the leaves of the trees blocking sunlight from reaching the bottom. But today the tree cover is sparse and sunlight bleeds through the canopy, allowing the growth of invasive species to outcompete native plants. The loss of native plants has led to a decline in several wildlife populations, including migratory birds.

Restoring the health of the trees would help the rest of the ecosystem recover. “We want to see more bald cypress leafrollers, little caterpillars,” said Erik Johnson, director of conservation science for Audubon Delta. 

Scientists like Johnson conclude that swampland is suffering when they see dropping numbers of caterpillars and visiting birds, as has been the case in Maurepas for decades. “We really haven’t seen outbreaks of those caterpillars in about 20 years, and corresponding to that we’ve seen a 50% decline in swamp songbird specialists like the prothonotary warbler,” he said.

In the 1970s and early ‘80s, the Maurepas Swamp was considered a haven for mallard hunting. The understory below the tree canopy still supplied enough food for the ducks to take refuge for the winter. As tree health declined, invasive salvinia, an aquatic weed native to South America, blanketed the water in dense mats below trees, choking off the native plants. 

Left without their usual food, the mallards were gone by the late 1980s, Johnson said.

With Tuesday’s groundbreaking, the construction project is beginning with almost no opposition, a stark contrast to the controversial and now-delayed Mid-Barataria Sediment Diversion, which has often been touted as the largest coastal restoration project in the country by environmentalists. 

With the Barataria project, Governor Jeff Landry has sided with commercial fishermen and other critics who argue that the river reintroduction would change the ecology of the Barataria Basin, devastating people who fish there and Louisiana’s very culture.

The two projects are very different, though they both divert river water into wetlands and play key roles in Louisiana’s Coastal Master Plan. 

For one, the Mid-Barataria Sediment Diversion is designed to build land, through sediment dropped from Mississippi River water that could create up to 26,000 acres of wetlands in Plaquemines Parish. 

The Maurepas Swamp River Reintroduction focuses only on moving nutrient-laden fresh water into the swamp, to revitalize the health of the cypress-tupelo forest and wetlands.

The Maurepas diversion also takes far less water from the river – it is predicted to move less than 5% of fresh water entering the Pontchartrain Basin, which amounts to less than 0.5% of the average Mississippi River flow. The diversion’s maximum flow is 2,000 cubic feet per second and is expected to run less than six months annually.

This freshwater diversion is designed to mimic seasonal spring flooding, which is essential to cypress trees’ life cycle. The seedlings require access to fresh water and a dry period to germinate. The trees also need nitrogen to grow, which is currently missing from the swamp but would be brought in through the river reintroduction, said Miller.

To track the success of the Maurepas river reintroduction, the United States Geological Survey (USGS) established five performance measures. If done correctly, the new “conveyance channel” – an artificial channel designed to move water from one place to another –  will mimic the flood and drought conditions of the Mississippi River, reduce saltwater intrusion that kills cypress trees, and increase soil elevation within the swamp while increasing forest structural integrity and facilitating nutrient uptake by native plants.

The differences will likely be visible to scientists keeping an eye on Maurepas forests. “I expect an increase in canopy cover as the trees put on more leaves and wood,” said Gary P. Shaffer, professor of biological sciences at Southeastern Louisiana University. 

Beyond giving more heft to existing trees, Schaffer finally expects to see new trees. “Natural seedling regeneration should also occur for the first time in decades so the forests will become denser and their soils will become stronger,” he said. 

A new partnership in mitigation for the Army Corps’ flood protection project

Until today, Mississippi River reintroductions have focused on building land within marsh wetlands, which contain fewer trees, relying on grasses like smooth cordgrass, marshhay cordgrass and California bulrush, alongside other herbaceous plants. The Maurepas freshwater diversion will be the first to rehabilitate nearly 45,000 acres of degraded and submerged “swamp forest,” where bald cypress, water tupelo and red swamp maple create native canopies.

But that’s not the only unique aspect of the Maurepas Swamp project. For the first time, CPRA has partnered with the Army Corps of Engineers to use the river reintroduction as mitigation for the West Shore Lake Pontchartrain (WSLP) flood protection project. 

To create the WSLP system, the Army Corps will build levees, floodwalls and pumping stations to protect communities along the east bank of the Mississippi River, in St. Charles, St. John the Baptist and St. James Parishes. Once the projects are completed, the new levee will meet with the Maurepas Swamp’s new conveyance channel in Garyville. The revitalized swamp forest will also help to further protect the River Parishes from storm surge and flooding.

But to protect the River Parishes, WSLP will build 18.5 miles of new levees, further disconnecting the Mississippi River from the Maurepas Swamp. To protect the surrounding ecosystem, the Army Corps is now required to “mitigate” the impacts of its new construction through the creation of new wetlands or the purchase of credits in a mitigation bank.

“The West Shore levee is impacting a lot of wetlands,” said Miller of CPRA. “And when you impact wetlands you have to mitigate for them.”

In January 2023, the Army Corps formalized a partnership with CPRA to use 9,000 acres of the swamp as a mitigation area for the flood protection project, by creating the new channel that reconnects the river to the swamp. 

The Army Corps will monitor the ecological progress of this swampland to ensure that the river reintroduction works as intended. Louisiana will monitor the entire 45,000-acre project area for at least 50 years, Miller said.

Bringing the two projects together took a lot of work, said Renfro of the National Wildlife Federation. But now, construction for both will take place concurrently, and she is hopeful that Maurepas Swamp will serve as a proof of concept for future collaborations between the Army Corps and CPRA.

Through one project, it became possible to achieve two goals, Renfro said. The Army Corps knew it needed to make up for impacting swamp with its levee project. And this part of the Maurepas Swamp happened to fit that bill, because it was located in the footprint of the levee project and badly needed a new chance at life. 

Two goals, now meet in one project. “The stars aligned,” Renfro said.