The saltwater wedge is continuing to creep up the Mississippi River, but it isn't expected to reach New Orleans or threaten its water supply.
The U.S. Army Corps of Engineers said that, thanks to a brief increase in the flow of the river over the last week, the salt water was pushed back a few miles, to just south of Myrtle Grove in Plaquemines Parish, where the agency is building an underwater sill to prevent the salt water from moving further upriver.
Corps spokesperson Ricky Boyett said on Wednesday that construction of the sill is nearly complete and will be finished by Oct. 12. The salt water is expected to reach the sill by Oct. 18.
"We still need rain in the river valleys," Boyett said. "The sooner the better."
A saltwater wedge is the phenomenon of salt water moving up the Mississippi River from the Gulf of Mexico when the river flow decreases due to drought. The New Orleans metro gets its drinking water from intakes in the Mississippi River. Salt water can damage municipal water systems and corrode pipes, causing lead to leach into supplies.
High levels of salt in drinking water is also a problem for vulnerable populations, including pregnant women and those with liver or kidney conditions.
While the wedge likely won't progress as far as it did in 2023, when it overtopped the sill and was projected to reach New Orleans, river levels will continue to drop over the next month.
The river is now flowing at 215,000 cubic feet per second. That's expected to drop to 160,000 cubic feet per second in the next month. The Corps needs that flow to double -- to 400,000 cubic feet per second, enough to wash away the underwater sill and push salt water back out into the Gulf.
Last month, the National Oceanic and Atmospheric Administration reported that drought in the Ohio River Basin since early August has contributed to low water levels in the Mississippi. Normally, the Ohio River supplies about half of the water in the lower Mississippi, but is currently contributing only about 8%.
Because of the ongoing government shutdown, NOAA is not providing current updates on how drought is affecting water flows on the lower Mississippi.
The river is about 2 feet 10 inches above sea level at the Carrollton gauge in New Orleans, and it is projected to remain at about that depth for the next month.
Climate change is projected to increase extreme weather events in the Mississippi River Basin and lead to more severe droughts and floods.
Prior to 2022, the Corps had built a sill to prevent the upriver movement of salt water only three times, in 1988, 1992, and 2012. It has now built the sill for four consecutive years.
Lower Plaquemines Parish has repeatedly been on the front lines of the problem, having in previous years provided bottled water to residents over the course of several months. The Corps also brought in supplies on barges in 2023.
The parish has more recently prepared for saltwater intrusion by putting infrastructure in place to pump supplies down from Belle Chasse or by procuring reverse osmosis filtration machines.