Work begins on giant underwater dam in Mississippi River to block advancing saltwater

Construction has begun on an underwater dam in the Mississippi River in Plaquemines Parish to stop saltwater that is advancing from the Gulf of Mexico and threatening drinking water supplies, the Army Corps of Engineers announced Wednesday.

The dam, or sill, is being built across the river bed near Myrtle Grove, with initial plans for it to be 55 feet high. It is the second year in a row that the Corps is building a sill due to saltwater intrusion, the result of an extremely low Mississippi River.

Gov. John Bel Edwards has already declared an emergency for Plaquemines Parish, which draws drinking water from the river. The Boothville water system, which serves residents and businesses south of the Empire Bridge in the parish, has been contaminated with high levels of sodium and chloride, the two minerals that make up salt.

The parish has been distributing water, with the salt potentially harmful to those on low-sodium diets or dialysis.

Weeks Marine has been contracted to build the sill, which will erode naturally when higher river levels return, the Corps said. Construction began on Tuesday.

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