A partial opening of the "seems a certainty now," Louisiana State Climatologist Jay Grymes said in emailed comments Thursday, as recent forecasts indicated a further rise in the level of the Mississippi River.
The opening, which is determined by the U.S. Army Corps of Engineers, would likely begin next week, according to Grymes. He said that the question now is how long the spillway may need to divert river water into Lake Pontchartrain.
"When we look at how the rate of flow has been going up over the past three to five days, it's probably going to get to that critical threshold," Grymes said, meaning that a spillway opening is "very likely."Â Â
The Corps has not announced a Bonnet Carré opening, and officials said they are continuing to monitor the forecast. The agency typically declares an opening around two days before the operation would begin, said Matt Roe, a spokesperson for the New Orleans district.
According to National Weather Service forecasts as of Thursday morning, the river will crest in New Orleans at 16.9 feet on May 2 and then gradually drop in the following days.
The spillway, located in St. Charles Parish, is typically opened by the Corps when the river flow rate hits 1.25 million cubic feet per second, which usually corresponds to a river level of around 17 feet on the Carrollton gauge in New Orleans. But at this phase in the flood cycle, higher flow rates are translating to slightly lower elevation, said Roe. An opening might be triggered at 16.5 or 16.6 feet.
People fish in the Bonnet CarrŽ Spillway as the U.S. Army Corps of Engineers conducts a test opening in Norco, La., Monday, April 21, 2025. The test comes as the Mississippi River nears flood stage and could lead to the first official opening of the spillway since 2020 if conditions warrant. (Staff Photo by David Grunfeld, The Times-Picayune)
This would be the first time the Bonnet Carré has opened since 2020.
The river has been rising over the past couple months, which is common in the spring as rainfall from storms in the Midwest and South trickle down to Louisiana. Earlier this week, the Corps ran a "" of one of the 350 bays that compose the spillway in anticipation of a potential opening.
Mississippi opposed to spillway opening
Opening the spillways alleviates pressure on the levee system in south Louisiana, but the rush of fresh water into the lake can hurt commercial shrimp and oyster fisheries.
The Mississippi Sound Coalition, representing local governments, fishers and the tourism industry, sent a letter to the Corps last week urging the agency to limit any spillway opening due to these potential harms.
"Operations of the Bonnet Carré Spillway in flood years like 2011 and 2019 have caused extreme adverse effects on the oyster reefs, dolphins, fisheries and natural resources of the Mississippi Sound," it said in a statement. "The openings in 2019 alone essentially wiped out many natural oyster reefs in the Sound."
Mississippi Lt. Gov. Delbert Hoseman sent a letter to the Corps objecting to a spillway opening, saying that repeated freshwater diversions "have devastated Mississippi's coastal ecosystem, crippled our seafood industry, endangered public health, and severely harmed our tourism economy."
