Louisiana has new plans for the tail end of the Mississippi. After decades of building levees along its banks, the state now hopes to cut a hole in the river's edge and siphon off a large flow of sediment and water into the nearby Barataria Basin, south of New Orleans. This would help rebuild the coastline in an area with one of the highest rates of land loss in the world.

Where the river exits into the Gulf of Mexico in Plaquemines Parish, the land has been reduced to a narrow spit, improbably jutting into the open water like a knife balanced off the edge of a table.

The $1.3 billion Mid-Barataria diversion project is the largest of the sediment diversions outlined in the Louisiana's $50 billion 2017 Coastal Master Plan , unanimously passed by state lawmakers in June and widely supported by environmentalists, scientists, and restoration groups across the state. But fishermen and communities in the crosshairs worry that the project could upend a lifestyle going back generations.

Between 1932 and 2010, Louisiana lost more than 1,800 square miles of coastland to a myriad of factors, including sea level rise, subsidence (land settling or sinking), and oil industry development. If wetland loss were to happen at a constant rate, it would amount to about a football field every hour, according to a 2011 estimate . Though it's slowed since then, the latest study from the US Geological Survey, published in July, found the rate is now a football field every 100 minutes.

Yet it's an process as old as the river itself—which, long before the levees, regularly deposited water and silt into the nearby land when the banks flooded. Some were dreaming of this project at least as far back as 1989, when the newly formed non-profit Coalition to Protect Coastal Louisiana first begged the state's lawmakers to "think boldly" to combat the already alarming rate of coastal land loss with one major, cornerstone request: Divert water and sediment from the Mississippi into the surrounding marshland.

The Mid-Barataria diversion is still at least five years away from breaking ground, as construction waits for extensive environmental reviews required by the National Environmental Policy Act.

The master plan calls for 124 separate projects over 50 years, which together are expected to maintain or build 800 square miles of land, saving the state a total of $8.3 billion in economic damage that might otherwise inflict the people, industries and communities along the coast.

Neither the state nor Army Corps of Engineers have attempted to suck sediment from the river before.

An illustration shows tanker traffic on the Mississippi passing by the planned Mid-Barataria sediment diversion. Image: Coastal Protection and Restoration Authority of the state of Louisiana

Nearly three decades later, thanks to the full backing of the state's politicians, Louisiana is poised to take on the task.

"The state and the nation will either act now to save Louisiana's four million acres of coastal wetlands—forty per cent of the nation's coastal marshes—or lose them forever," the coalition warned in its starkly titled report: Coastal Louisiana, Here Today and Gone Tomorrow?

"All the organizations that we work with believe that the master plan is an absolute godsend, and it's a blueprint to do the work that needs to be done," said Jimmy Frederick, the coalition's communication director. As lawmakers approved the plan, Kimberly Davis Reyher, the executive director, said the mid-Barataria diversion "may very well be the most important environmental construction project in the history of our country."

"They're going to hit us in the heart. They're deserting us"

It comes as research shows that in addition to faster rising sea levels, the land is sinking more quickly than expected. In June, scientists published the most intricate map to date of the rate of subsidence across the coastline, finding that while previous estimates suggested a rate of 6 mm per year, it's actually an average of 9 mm.

"That doesn't sound like very much, but you have to compare it against the fact that Louisiana is really low," said Jaap Nienhuis, the study's lead author and a researcher at Tulane University. "So if it's only a few inches above the high tide line, then 9 mm brings you to that point within a decade."

The Mid-Barataria sediment diversion will be massive: Diverting as much as 75,000 cubic feet per second of water and sediment, a flow greater than the 50,000 cubic feet of the Niagara Falls in its off season.