NEW ORLEANS (AP) — With the Mississippi River running at low levels, salt water is moving up from the Gulf of Mexico.

Denser, heavier saltwater flows upriver beneath fresh water flowing downstream when the river’s flow drops below normal. The Army Corps of Engineers says salt water is not yet considered a threat to water supplies in the New Orleans area.

If forecasts show the salt water is four weeks away from fouling freshwater intakes in the New Orleans area, the corps it will attempt to block the saltwater by building an underwater sill of dredged sediment.

However, Will Veatch, a corps hydrologist, says the corps does not believe the salt will get far enough upriver to warrant building a sill.

Veatch says the corps’ sill decision will be triggered by the river’s height and speed of its flow at Red River Landing, above Baton Rouge.

The Red River Landing water level is at 17.1 feet, and it is forecast to drop to 13.5 feet by Aug. 8. Veatch says a forecast of 10 feet would be required to trigger the sill construction.

Meanwhile, Plaquemines Parish officials say they have measured elevated salinity levels at water intakes in Boothville and Venice.

But Veatch says the lower end of the parish has access to freshwater from a pipeline from Belle Chasse. The pipeline was installed after low river events in 1988 and 1999.