NEW ORLEANS, Louisiana -- Gov. Bobby Jindal on Wednesday declared a state of emergency for Plaquemines Parish as it deals with encroaching salt water that's threatening drinking water in the New Orleans area.

The declaration clears the way for state agencies to offer help to the parish as it deals with its water supply issues. Due to the Mississippi River's low water levels, salt water has been moving far upriver and was at the outskirts of New Orleans by Wednesday, nearly 90 miles north of the mouth of the Mississippi. Also Wednesday, Plaquemines Parish issued an advisory to parish residents that high levels of sodium and chloride were being measured in drinking water.

The river was closed temporarily to shipping traffic as contractors began building an underwater barrier that the Army Corps of Engineers says will stop the advance of salt water. Many communities along the river draw freshwater from the Mississippi with freshwater intakes and water treatment facilities that are incompatible with saltwater caused by the current intrusion.

The Governor's Office of Homeland Security and Emergency Preparedness is providing 30,000 bottles of water to the parish over the next several days, at the parish's request. The Louisiana National Guard will deploy a truck that contains 4,000 gallons of water to the parish Thursday and will continue to provide this same supply for five days, officials said.

River traffic had to be closed for about three miles while the Great Lakes Dredge & Dock Co., installed a pipeline needed to build the massive underwater sill. The river was expected to reopen Wednesday evening.

The company will dredge sediment to build up the barrier at a point near Myrtle Grove in Plaquemines. The company was given an $8.1 million contract to do the work. The barrier is expected to be done in 45 days.

Ricky Boyett, a corps spokesman, said the sill will begin pushing the salt water back into the Gulf of Mexico in about two weeks. The salt water is expected to be stopped by the sill and then pushed out by the flow of the river. The corps says underwater sills have stopped salt water intrusion in the past. Sills were constructed in 1988 and 1999.

Typically the rush of freshwater down the Mississippi River keeps salt water contained to the southernmost portions of the river. But in times of drought the Gulf's salt water can move farther inland. The river's stage has been a couple feet below the mean average at New Orleans.

During the construction of the barrier, river traffic will be reduced to one lane as it passes the construction zone, Boyett said.

Matt Gresham, a spokesman for the Port of New Orleans, said the port's operations would not be slowed down by the sill work. He said Wednesday's temporary closing had left shippers mostly unaffected.

The sodium and chloride levels being measured in Plaquemines were not considered a health threat but people on dialysis, on low-sodium diets, with high-blood pressure and suffering from kidney diseases were being advised to consult with their doctors.

Caitlin Campbell, a Plaquemines spokeswoman, said the parish was pumping water from Belle Chasse to southern parts of the parish to dilute the sodium and chloride. The parish also was ready to bring drinking water downriver by barge, she said.

"We're not going to let our citizens go without drinking water," Campbell said.