New Orleans is prepared for a drinking water emergency from the drought-stricken Mississippi River

Louisiana officials are in a race against time as salty water from the Gulf of Mexico threatens drinking water supplies in New Orleans and surrounding areas due to unusually low water levels in the drought-stricken Mississippi River.

New Orleans Mayor LaToya Cantrell signed an emergency declaration Friday in response to concerns that salt water entering the river could affect the availability of safe drinking water in the coming weeks.

The situation highlights the dangers of saltwater intrusion to communities in southeast Louisiana and adds to broader concerns about climate change and the availability of safe drinking water in drought-prone parts of the state.

Stephen Murphy, an associate professor at Tulane University’s School of Public Health and Tropical Medicine, estimated that nearly a million people in the New Orleans metropolitan area could be affected if the Mississippi River remains low.

Although forecasts are subject to change, saltwater could reach Belle Chasse intakes by October 13 and New Orleans facilities later in October.

About 2,000 residents in Plaquemines Township, south of New Orleans, were already using bottled water this summer after saltwater seeped into the area’s water systems.

Too much salt in drinking water can cause an increase in sodium in the body, which raises blood pressure.

Persistent drought conditions have kept the Mississippi River at unusually low levels and greatly weakened its flow, Murphy said, adding that the region’s unique topography has made the situation even more difficult.

The mouth of the Mississippi River is located well below sea level, which means that some of the salty water from the Gulf of Mexico naturally creeps inland. Salt water is denser than fresh water, so it flows as a wedge along the riverbed below the Mississippi’s fresh water.

In normal times, the downstream flow of rivers is powerful enough to stop the encroaching salt water, preventing it from moving too far inland. Severe drought conditions have caused water levels in Mississippi to drop to one of the lowest levels in decades.

Murphy said the river’s flow rate is no longer able to combat the saltwater wedge. On a normal day, it’s strong enough to keep the salt water at bay, but we’ve just seen the water coming down this far south downstream.

Saltwater intrusion in the lower Mississippi River becomes a problem when river flows drop below 300,000 cubic feet per second, scientists have said. As of last week, the flow rate was 148,000 cubic feet per second, according to Murphy.

At a news briefing Friday, Louisiana Gov. John Bel Edwards said a lack of rainfall was to blame for the rivers’ woes.

He said in a statement released Friday: Unfortunately, without the relief of dry weather, we are beginning to see saltwater intrusion creep upriver, despite efforts by the Army Corps of Engineers to mitigate the problem.

This week, the Army Corps is expanding an underwater barrier that was first built in July to slow the intrusion of salt water upstream. The barrier, known as a threshold, functions similarly to an underwater barrier. If conditions remain dry, the threshold will most likely be crossed again, Murphy said.

He said we tried our best to delay the formation of this wedge of salt water moving north and to give time until hopefully Mother Nature intervenes, but also to help us get assets and resources to offset some of that salt water.

State officials said they are working with municipalities to test water supplies and monitor changes. The Army Corps also said millions of gallons of water would be brought in to dilute local water supplies if necessary.

The Corps is securing water barges to support affected water treatment facilities by transporting water collected from parts of the river that do not have salinity readings, Col. Cullen Jones, the Corps’ New Orleans District commander, said in a statement Monday. This water can then be combined with water at the municipal plant to create a safe mixture for processing.

Murphy said the regions’ drinking water problems are part of a larger narrative about drought and drinking water availability in a warming world.

This is something we can no longer ignore, he said. We had an extremely hot season, we had a heat dome in the southern states and we had warmer than average temperatures across the globe. It’s unfortunate, but sometimes it takes a moment of crisis to bring attention to these things in our own backyard.