JACKSON, Miss. (AP) — Opening a spillway as a flood-control measure in 2019 sent polluted fresh water from the Mississippi River into the Gulf of Mexico and killed bottlenose dolphins that live in saltwater, according to a new lawsuit.

Several local governments and business groups on the Mississippi Gulf Coast filed the federal lawsuit Monday against the U.S. Army Corps of Engineers.

The lawsuit argues that the Marine Mammal Protection Act requires federal agencies, including the Corps of Engineers, to obtain a U.S. Department of Commerce permit when their actions may disrupt the behavioral patterns of an animal such as the bottlenose dolphin.

“The massive volumes of polluted fresh water diverted through the Bonnet Carré Spillway and into the Mississippi Sound caused direct and indirect mortality of resident bottlenose dolphins,” the lawsuit says. “Many of the dolphins that did survive developed extremely painful and debilitating skin lesions.”

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The lawsuit seeks a court order that would require the Corps of Engineers to comply with any obligation to obtain a permit before any further opening of the Bonnet Carré Spillway — something that could slow down use of the flood-control structure.

The Associated Press sent an email Wednesday to the U.S. Department of Justice, which represents the Corps of Engineers, seeking comment on the lawsuit. The department did not immediately respond.

The Bonnet Carré Spillway is upriver from New Orleans. Opening the spillway diverts Mississippi River water to Lake Pontchartrain and Lake Borgne, after which it flows to the Mississippi Sound in the Gulf of Mexico.

It is rarely used. But when the river is high, opening the spillway eases pressure on the levees that protect New Orleans.

However, opening the spillway also carries pollutants and nutrients into the Mississippi Sound and reduces salinity. The result can be damage to oyster, fish and crab habitats, and algae blooms that affect marine life and beaches.

Opening of the Bonnet Carré Spillway has caused conflict between leaders in Louisiana, who want to protect the state’s largest city, and those in Mississippi, who want to protect fisheries and other commercial interests that rely on the Gulf of Mexico.

The new lawsuit is similar to one that some of the same coastal Mississippi governments and business groups filed in 2019 against the Corps of Engineers. The earlier lawsuit said the corps was required to consult with the National Marine Fisheries Service before opening the spillway.

In January 2023, U.S. District Judge Louis Guirola Jr. of Gulfport, Mississippi, ruled in favor of those who sued. The 5th U.S. Circuit Court of Appeals affirmed that ruling in June.