Contractors will build the sill to an elevation of -55 feet. At that height, USACE says they will monitor the progression of the saltwater wedge to determine if additional height

Construction has begun on a saltwater sill near Myrtle Grove to help mitigate the effects of saltwater intrusion up the Mississippi River.

The sill, or underwater levee, is being built for a third year in a row to head off the potential for New Orleans area drinking water to be threatened.

It's happening for a third year in a row in lower Plaquemines Parish. Officials say they now have to treat it like hurricane preparations.

As the Mississippi River water level lowers, the possibility of a saltwater intrusion increases, and for the third year in a row, southern Louisiana will be facing one.

Salt water is moving upriver from the Gulf of Mexico. Drought in the central United States has weakened the mighty river’s flow to the point that it can no longer push out saltier water from the Gulf. For Plaquemines Parish, which draws directly from the river, this intrusion is a threat to its water source.

For the third year in a row, seawater creeping up the Mississippi River is threatening the drinking water supply in and around New Orleans.