As a historically high Mississippi River rolls through Louisiana, straining an 80-year-old system of levees and spillways, ecologists lament a missed opportunity in all those muddy waters.

It’s dirt.

The high river carries millions of tons of mud, sand and silt swept down from the cornfields of Minnesota through the delta plains of Mississippi. Most of it will shoot past New Orleans and straight into the deep waters of the Gulf of Mexico.

But in the lowlands of Louisiana, dirt is gold. Sediment built the state over the centuries, piling up at the bottom of the continent’s longest river, pushing into new channels. As the river wandered, the land rose.

That process was subverted by the straitjacketing of the Mississippi in the name of commerce. Hemmed in by levees, the river shunts most of its sediment out over the edge of the continental shelf, draining swamps, reducing coastal protection from hurricanes and contributing to the disappearance of about 1,500 square miles of Louisiana coast over the past century.

Ecologists and state officials want to re-engineer the river to rebuild the land. Ambitious plans would reconnect the Mississippi to its surroundings by opening levees at key points and sending splashes of the river — and the dissolved land it conveys — back to the sunken areas.

“We want to grab every opportunity to put sediment into the wetlands,” said Robert Twilley, an ecologist at the University of Louisiana at Lafayette.

Although such plans have been debated for decades, the triple-whammy of hurricanes Katrina and Rita in 2005, the BP oil spill last year and this year’s bulging river have reinvigorated advocates. They say that strategically opening the Mississippi offers its own triple-whammy of benefits: It restores damaged ecosystems, reduces pressure on river levees during floods and builds new coastline that buffers against hurricanes.

In 2007, a new Louisiana state agency formed in the wake of the 2005 hurricanes adopted such a strategy. In a comprehensive plan that remains mostly unheeded, the Coastal Protection and Restoration Authority recommended using “the majority of the [Mississippi] river’s sediments and fresh water to both create new delta . . . and nourish existing wetlands.”

But a lack of federal funding has stymied such a radical re-engineering.

“The idea of using the river to restore the coast in a major way has been on the table for a long time,” said Denise Reed, who studies the issue at the University of New Orleans. “But it hasn’t moved forward.”

The most ambitious project — to dig a new, 100-mile river channel west of New Orleans — is politically dead on arrival. Priced at $1 billion to $3 billion and planned to cut across some wetlands, the “third delta” project was too big to attract sufficient support.

The one Mississippi River diversion that does exist proves that such an approach can work, said Simone Maloz, director of the nonprofit organization Restore or Retreat, which advocates wetlands restoration. In north Louisiana, a huge gateway called Old River Control shunts 30 percent of the Mississippi River to the west, where it joins the Atchafalaya River. The combined flow carries sediment to the foot of the state. Since 1970, the extra sediment has built about 18 square miles of new land in the Wax Lake Delta, Maloz said, providing more hurricane protection for nearby Morgan City.

The diversion also lowers the Mississippi, reducing flood heights.

Even smaller-scale projects can help, said Steven Peyronnin, director of the nonprofit Coalition to Restore Coastal Louisiana. His group proposes rebuilding the Bonnet Carre Spillway north of New Orleans. Opened last week to relieve pressure on river levees, the spillway diverts a sixth of the Mississippi into Lake Pontchartrain, eventually pouring into the gulf.

Peyronnin advocates lowering the spillway’s gates so they could also be opened during normal river flows, allowing water and sediment to flow into the surrounding wetlands.

Peyronnin and other advocates acknowledge that the current approach has been hugely productive: The Mississippi sends waves of grain barges south, and oil, seafood and imported goods to the north. But shipping can be maintained even with extra river diversions, Reed said.

That’s because diverting sediment above the busy ports of Baton Rouge and New Orleans would reduce the amount of dredging required to maintain the deep-draft shipping channel. This week, in anticipation of extra sediment, the Army Corps of Engineers sent additional dredging vessels to New Orleans. Restoration advocates want the corps to pipe those dredgings into the wetlands. “That would be a good start,” Peyronnin said.

But just a start. If mankind doesn’t send more of the river toward the land, nature eventually will, said John Day, emeritus professor of coastal sciences at Louisiana State University.

In just 18 years, in 1993 and 2011, the Mississippi has experienced two so-called 500-year floods. Climate scientists warn that more are on the way. “Big floods are going to become more common” because of climate change, Day said. “In the future, we’ll lose control of the river.”

Residents of Cajun country are now getting a taste of such a historic flood. On Saturday, the Army Corps began opening the Morganza Spillway to lower the river for the first time since 1973. A torrent of water now flows toward about 25,000 central Louisiana residents, who have been urged to evacuate. On Tuesday, Louisiana Gov. Bobby Jindal (R) said the floodwaters were moving more slowly than expected, even as construction crews hurried to erect miles of flood barriers, according to Reuters.

Later Tuesday, the Coast Guard reopened the Mississippi north of New Orleans, to let vessels pass by one at a time to help reduce pressure from the rising waters.