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The marshes south of New Orleans are dying, slowly sinking into the rising sea. But when Erik Johnson imagines their future, he sees a paradise for birds. Bald Eagles will feast on fish in Barataria Bay. Green-winged Teal and Mottled Ducks will forage in the shallows. With luck, Roseate Spoonbills might join in. “Where the freshwater and saltwater mixes is just a really productive system,” says Johnson, director of conservation science for ̽����ѡ Delta.

That wildlife haven is within reach, he and other conservation advocates say, if Louisiana moves forward with one of the biggest coastal-restoration projects in history. The will help to rebuild vanishing habitats in an important area for a variety of birds; Johnson co-authored estimated that coastal Louisiana supports nearly three-quarters of the country’s Sandwich Tern population and more than half of the world’s Seaside Sparrows. At the same time, the project promises to provide a buffer from flooding and hurricanes, potentially shaving a foot off of storm surges near New Orleans within 50 years.

The diversion is a core component of Louisiana’s five-decade, to protect its coast. “It’s a critical project for our state,” says Kristi Trail, executive director of Pontchartrain Conservancy. “It’s one key way we know that will restore the coast to the way that Mother Nature designed it to be.”

To do so, the state wants to mimic the natural processes that created the marshes. But reviving the ecosystem’s past will have costs for people who have built livelihoods around what exists today.

For thousands of years the Mississippi River’s flow replenished coastal wetlands with fresh water and sand, silt, and clay from upstream. But levees built over the past 300 years channeled the river out into the Gulf of Mexico, cutting off the supply of land-building material. In more recent decades, canals dug by oil and gas companies have eroded the coast. And the 2010 Deepwater Horizon explosion leaked oil into Barataria Bay and nearby salt marshes, killing as many as 1 million birds and accelerating erosion by suffocating grasses that held the land in place. As a result, Louisiana has lost more than 2,000 square miles of coastal land since the 1930s—an area around the size of Delaware—and sheds the equivalent of a football field every 100 minutes. The Gulf has claimed about 430 square miles of land in the Barataria Basin alone, and will devour that amount again in the next 50 years without intervention.

To prevent further land loss, Louisiana plans to create an opening in the Mississippi River levee south of New Orleans and turn the flow of sediment back on through a conveyance channel. Money from an oil-spill settlement with BP would fund the $2 billion diversion. A March estimated that, in the Barataria Basin, the project would build up to 27 square miles of land by 2050 and rescue 17 percent of land that would otherwise be lost to sea-level rise by 2070.

The analysis paints a grimmer picture, however, for some commercial fishers and coastal residents. The influx from the Mississippi would dilute the mix of fresh- and saltwater that helps make Barataria Bay a major oyster and brown-shrimp fishery. “The adverse impacts are going to be so far-reaching,” says Captain George Ricks, a fishing guide and president of the Save Louisiana Coalition, which opposes planned diversions.��

Some coastal residents also worry they’ll face more flooding. While the diversion is expected to decrease storm surge north of the opening in the levee, it will likely make it worse to the south as river water flushes toward nearby communities. The project could raise the average water level by up to one foot around Lafitte and near Grand Bayou, where members of the Atakapa-Ishak Chawasha Tribe live, models show.

Louisiana plans to set aside $33 million for new oyster seed grounds, refrigeration for shrimpers who will have to travel farther into the Gulf, or other measures to help fishers adapt to the diversion’s effects. The state may also buy out or help elevate homes faced with more flooding. But that isn’t enough for those who see no clear middle ground. Citing concerns about the economic impact to fishers, elected officials representing Plaquemines Parish, the county where the diversion would be built, voted unanimously in April to oppose the project.

A public comment period that ended in June allowed residents and others to weigh in on the environmental analysis before the state decides what happens next. Construction could begin as soon as next year. There’s no outcome that will satisfy everyone, and even the diversion’s advocates acknowledge that it won’t protect the coast forever; by 2070 rising seas are expected to whittle the land it creates in the basin from 27 square miles down to 21. Long-term, coastal decision makers will confront increasingly difficult choices about what to protect. “But if we do nothing,” Johnson says, “the sea will continue to rise, putting everyone at greater risk.”

This story originally ran in the Summer 2021��issue as “Forward Marsh.”​��To receive our print magazine, become a member by��.