Officials again monitoring salt water in Mississippi River as possible drinking water threat

The latest: The Army Corps of Engineers measured the salt water "toe," or leading point, at river mile 23.6 late last week, creeping north by a mile and a half over about two days, according to Army Corps spokesman Matt Roe.

• The water in south Louisiana remains safe to drink.

Yes, but: "We're in the traditional low-water season right now," Roe says, and though the toe "hasn't progressed as far as it had at this point last year … we're just past that threshold to go out and measure monitoring of it."

Catch up quick: Saltwater intrusion had southeast Louisiana on edge late last summer, as a briny wedge of water from the Gulf of Mexico crept up the Mississippi River.

• Some Plaquemines Parish communities spent months drinking bottled water, though the salt stopped short of the more populous New Orleans metro.
• The metro area's water was deemed safe from the threat by mid-October, but not before complicated plans had been rushed together to keep regional taps flowing.
• But officials warned that the 2023 saltwater intrusion would likely repeat as climate change shifts weather patterns and expectations for what's "normal."

How it works: As the Mississippi River empties into the Gulf of Mexico, the flow of fresh water typically provides enough pressure to keep salt water from creeping up the river.

• But drought conditions, especially north of Louisiana, lead to lower water pressure in the Mississippi River.
• Because salt water is denser than fresh, it moves north along the river bed, threatening water supplies.

State of play: A few things have changed at the Army Corps since last year's emergency created something of a roadmap, Roe tells Axios New Orleans.

• The Corps now has a "trigger" in place to know it's time to start procuring freshwater for impacted communities if the salt water is expected to be at river marker 65 within the Corps' standard 28-day forecast.
• A trigger to build an underwater levee, called a sill, to help block the salt water also gets activated if salt is expected at river mile 65 within a 10-day forecast and at river mile 80 within the 28-day forecast.

What's next: The Army Corps will update its measurements twice weekly until conditions improve.

The bottom line: By this date last year, the Army Corps had already constructed the underwater levee. Conditions haven't yet made that a necessity, but it's worth monitoring.