GULFPORT, Miss. — A federal judge has dismissed a lawsuit that sought to protect dolphins along the Mississippi Gulf Coast after dozens were killed or sickened in 2019 following the prolonged opening of a spillway used for flood control.

U.S. District Court Judge Louis Guirola Jr. ruled Wednesday that local governments and business groups that filed the civil complaint in January had no legal standing to sue. The judge said the plaintiffs, who called themselves the Mississippi Sound Coalition, failed to show they faced imminent harm.

The coalition had sued the Army Corps of Engineers over its operation of the Bonnet Carre’ Spillway upriver from New Orleans. The spillway is used to divert Mississippi River water to Lake Pontchartrain and Lake Borgne, after which it flows to the Mississippi Sound in the Gulf of Mexico.

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When the river is high, opening the spillway eases pressure on the levees that protect New Orleans. However, it also flushes pollutants and nutrients into the Mississippi Sound and reduces salinity.

The coalition’s lawsuit said that polluted freshwater flowing into the Gulf in 2019, when the spillway for opened 120 total days, left dead and sickened bottlenose dolphins stranded along Mississippi beaches. One expert quoted in the lawsuit said 142 sick and dead dolphins washed onshore.

The coalition said the grisly sight tarnished tourism and seafood industries that are vital to the area’s economy.

The group’s attorneys argued the Marine Mammal Protection Act requires Army Corps and other agencies to obtain a U.S. Department of Commerce permit when their actions may kill, harm or harass animals like the bottlenose dolphin. They wanted a judge to order the Army Corps to seek permits before future operations of the Bonnet Carre’ Spillway.

The judge sided with the Army Corps in ruling that the coalition failed to show that it faces imminent harm from future spillway openings because their frequency and duration are unpredictable - as is the potential threat to dolphins.

The judge noted that the coalition presented no evidence that dolphins were harmed when the spillway was last opened in 2020, or during prior openings in 2018 and 2016.

“The possibility of future harm claimed by Plaintiffs is too speculative,” the judge wrote.

Robert Wiygul, an attorney for the Mississippi Sound Coalition, did not immediately reply to an email message Saturday.