Posted on October 20, 2025
USACE builds underwater saltwater barrier in 12 days on Mississippi River to protect New Orleans’ water supply. Barrier aims to prevent saltwater intrusion during persistent drought; maintenance ongoing to avoid corrosion of city’s drinking water system.
In an update to a story CEG posted earlier in October, the U.S. Army Corps of Engineers (USACE) has completed an underwater sill built to prevent salt water from moving up the Mississippi River and threatening New Orleans’ water supply.
The agency constructed the sill in only 12 days, finishing the construction on Oct. 10, USACE spokesperson Matt Roe told NOLA.com, the online edition of the New Orleans Times-Picayune.
The USACE started building the sill at the end of September. Referred to by the agency as a saltwater wedge, the new sill forms a continuous barrier across the river near Myrtle Grove in Plaquemines Parish, 55 ft. below the water’s surface.
Expectations are that the sill will successfully keep salt water from reaching the drinking water intakes upriver. It forms when the river is low, as it is currently, due to a persistent drought across the Mississippi Valley that is projected to continue through at least the next month.
“We continue to work closely with our state and local partners while measuring and calculating the location of the toe of the saltwater wedge and forecast river conditions,” Roe said to the New Orleans news source.
The USACE takes measures to prevent the salt water from moving upriver because New Orleans and surrounding communities get their drinking water from the Mississippi. Municipal water systems are not equipped to desalinate water, and salt water can corrode pipes and leach lead and other chemicals into the city’s drinking water system.
The federal agency said it does not have a final cost for the sill’s construction because its crews may have to continue dredging sediment to maintain it over the next several weeks.
The salt water in the Mississippi was pushed downriver a few miles due to heavy rains across the Mississippi Valley in the second full week of October, and another small bump in the river’s flow is projected during the week of Oct. 19 due to heavy rains forecast upstream in the Ohio River Valley.
But Roe noted that the river is still expected to drop over the next month from its current flow of 200,000 cu. ft. per second down to 160,000 cu. ft. per second, which will allow salt water to reach the sill around the end of October.
The current forecast does not call for the sill to be overtopped, or for the USACE to have to build the sill higher, as it did 2023 when the salt wedge nearly reached New Orleans’ water intakes, NOLA.com noted.
The Mississippi River was about 3 ft. above sea level at the Carrollton gauge in New Orleans on Oct. 16 and is projected to stay at that height for the next month.
During that time, the USACE will keep an eye on the wedge until the river flows at 400,000 cu. ft. per second, enough flow to flush the saltwater back out into the Gulf of Mexico and wash away the underwater sill.
This year marks the fourth consecutive year that the agency has needed to build the sill in the river to prevent saltwater from affecting municipal drinking water supplies. Prior to 2022, it had only built the sill three other times, in 2012, 1992 and 1988.
Climate change is projected to increase extreme weather events, raising the likelihood of both severe droughts and floods across the Mississippi River’s drainage basin, which extends across all or parts of 31 states and two Canadian provinces.
Downriver communities in Louisiana’s lower Plaquemines Parish are on the front lines of any issues with salt water. The Corps of Engineers used barges to bring in supplies to parts of the parish due to issues with salt water in 2023, and this year the parish prepared by procuring reverse osmosis filtration machines, which can filter salt from water.
