An influx of salt water in the Mississippi River, which feeds southeastern Louisiana's drinking water supplies, is once again creeping up the waterway. For the third year in a row, an underwater levee is being built to slow the brackish intrusion and prevent it from reaching water intake treatment facilities.

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

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.

On Monday, the U.S. Army Corps of Engineers, New Orleans District began construction of an underwater sill across the bottom of the Mississippi River channel to slow the progression of salt water from the Gulf of Mexico. Construction of the saltwater sill began in the river at mile marker 64 near Myrtle Grove, La.

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.

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