The U.S. Army Corps of Engineers has completed construction of an underwater sill near Myrtle Grove, Plaquemines Parish, to slow the upstream movement of salt water threatening New Orleans’ drinking water supply. The project, finished on October 10, took 12 days to build and now forms a continuous sediment barrier about 55 feet below the river’s surface.
The sill aims to block the saltwater wedge that forms during low-flow conditions in the Mississippi River. Drought across the Mississippi Valley has lowered river levels, allowing denser salt water from the Gulf to move inland. The Corps expects the saltwater wedge to reach the sill by the end of October but not overtop it.
The agency continues to monitor river flow and wedge location, coordinating with state and local partners. The current flow rate—about 200,000 cubic feet per second—is forecast to drop to 160,000 before rains in the Ohio Valley provide temporary relief. The sill will remain in place until higher flows flush the saltwater back into the Gulf.
The Corps has built similar sills seven times since 1988, with annual construction required since 2022 due to recurring drought conditions. Final project costs remain under review, pending additional dredging needed to maintain the barrier.