NEW ORLEANS – Louisiana’s coastal wetlands make up about 40% of all coastal marshes in the United States but according to Restore the Mississippi River Delta, an agency that provides technical guidance to the state and the U.S. Army Corps of Engineers, Louisiana loses between 25 to 35 square miles of coastal land each year. This equates to roughly one football field every 100 minutes.
While the levees prevent flooding, they also prevent new sediment from spreading to replenish the land. To better understand the enormity of the impact of natural sediment in building the coast, a team of scientists has examined a striking example at Neptune Pass.
A recent study led by New Orleans-based oceanographer, geologist, and climate scientist Alex Kolker, Ph.D., found that Neptune Pass near Buras, Louisiana, is forming one of the largest new deltas in North America.
“Neptune Pass is the largest new offshoot of the Mississippi River to form in nearly a century,” said Kolker who is associate professor at Louisiana Universities Marine Consortium. “It is building one of the largest new deltas in North America.”
In the meantime, the U.S. Army Corps of Engineers has suspended the permit for Louisiana’s Mid-Barataria Sediment Diversion project, citing concerns that the state “deliberately withheld” crucial information during the permitting process. This action follows a 90-day suspension of all work on the $3.1 billion project initiated in April 2025 by Governor Jeff Landry’s administration.
Louisiana could lose over $2 billion in funding if it does not commit to completing the project.
Wax Lake and Neptune Pass are both significant water channels in Louisiana, with Wax Lake located in St. Mary Parish in the southwest near Morgan City, and Neptune Pass situated in Plaquemines Parish in the southeast, about 70 river miles south of New Orleans.
While Wax Lake serves as a long-standing example of successful delta formation through engineered intervention, Neptune Pass offers a contemporary case of natural river dynamics contributing to wetland restoration. Both are part of Louisiana’s changing coast.
Mid-Barataria and Wax Lake Delta
The Mid-Barataria Sediment Diversion has been described as a cornerstone of Louisiana’s Coastal Master Plan. It aims to combat severe land loss by channeling sediment-rich water from the Mississippi River into the Barataria Basin. Proponents argue that the project is essential for restoring wetlands and providing storm protection while opponents, including local fishing communities, say it destroys fisheries habitats.
Where the Atchafalaya River meets the Gulf, a flow of sediment from a decades-old river diversion created land that grows by about half a square mile a year at Wax Lake Delta. Land is also being built by another diversion called West Bay and at the Bonnet Carré spillway.
Wax Lake Delta started when the U.S. Army Corps of Engineers dug a channel in 1941 to try to reduce flooding in nearby Morgan City, redirecting the flow of water from the Atchafalaya. This started the process of sediment buildup, noticed only after a massive flood in 1973 flushed a torrent of dirt down the river.
Neptune Pass
Prior to the 2019 high Mississippi River levels, Neptune Pass was a small channel. Between 2019 and 2021, this channel expanded and now carries 15% of the Mississippi River’s flow which is more than 100,000 cubic feet per second (cfs) when the river is in flood. This high flow brings sediments from the river’s enormous drainage basin to Louisiana.
Neptune Pass is currently building one of the largest new deltas in North America in Quarantine Bay. The Neptune Pass study found that 56-79% of the sediment material forming the Quarantine Bay Delta is new material from the Mississippi River.
“Between 2019 and 2022, six million cubic yards of sediment from the Mississippi River was diverted through Neptune Pass and deposited into Quarantine and Bay Denesse,” said Alisha Renfro, Ph.D., senior manager for Science Policy for National Wildlife Federation’s Gulf of Mexico Program. “This is twice the amount of material used in the nearby Grand Liard marsh creation project that restored 500 acres of wetlands.”
“In the past these high river flows have been major land-building events,” said Renfro. “Examples are Wax Lake after the 1973 flood and West Bay after the 2011 flood. Once the floodwaters dropped, new land was revealed, and we are likely to see that this year in Quarantine Bay.”
Kolker, whose research focuses on coastal systems, exploring how sea-level rise, sediment transport, and subsidence affect wetlands and deltas, has contributed to major environmental projects like the Mid-Barataria Sediment Diversion. “Our research shows that Neptune Pass is building land in a manner that follows the basic principles of delta geology,” said Kolker. “These same geological principles also underlie the diversions that are part of Louisiana’s Coastal Master Plan.”
The upshot is that if Louisiana does not harness the flow of sediment to manage coastal restoration, nature will determine the contours of the coastline for us. Sediment is the key resource for rebuilding wetlands and buffering against sea-level rise.
About Restore the Mississippi River Delta
Restore the Mississippi River Delta is working to protect people, wildlife and jobs by reconnecting the river with its wetlands. As our region faces the crisis of land loss, we offer science-based solutions through a comprehensive approach to restoration. Composed of conservation, policy, science and outreach experts from Environmental Defense Fund, National Audubon Society, the National Wildlife Federation and Pontchartrain Conservancy, we are located in New Orleans and Baton Rouge, Louisiana; Washington, D.C.; and around the United States. Learn more at MississippiRiverDelta.org and connect with us on Facebook and Twitter.
About the Neptune Pass Study
The Neptune Pass study was in-part funded by the National Wildlife Federation who is a coalition member of Restore the Mississippi River Delta. Also involved in this research were Alisha Renfro from the National Wildlife Federation, H. Dallon Weathers the Principal Consultant with hydrographic firm Delta Geo-Marine and Christy Swann, CEO and Founder of the Coastal Adaptation company RCOAST.
