The drought that has led to low levels along the Mississippi River is now threatening the quality of drinking water.

The river’s water levels have fallen to a point that it can’t flow with sufficient force to push back salt water from the Gulf of Mexico. As a result, the Army Corps of Engineers has been called into resupply water treatment plants in Plaquemines Parish, Louisiana, which has been overwhelmed by an influx of salt water.

The Army Corps, which already constructed a salt sill in the lower river, is now shipping fresh water from upstream to Plaquemines, on the extreme southeastern tip of Louisiana where the river meets the Gulf. The Corps has delivered 500,000 gallons by barge to the Port Sulphur Water Treatment plant to dilute the Mississippi’s salinity there, it said in a statement.

Drought across the central US and Midwest have left water levels low on not only the Mississippi but also its tributaries, such as the Ohio River. At Cairo, Illinois, the Ohio River is in its low water stage. Through September 26, nearly 55% of the Midwest was gripped by drought, with almost 66% of South also dry, according to the US Drought Monitor. More than 99% of Louisiana was in drought, according to the US Drought Monitor.

Low water can mean barges cannot carry as much freight up and down the river, which is a vital highway for shipping grains, oil, chemicals and raw materials. In fall, many crops harvested across the central US move by river barge.

In other weather news:

Atlantic: Tropical Storm Philippe could graze the Caribbean Islands of Antigua and Barbuda, where storm watches have been posted. Philippe has winds of 50 miles per hour and is 95 miles east-southeast of Barbuda.

Pacific: Typhoon Koinu is gaining strength east of Taiwan, where it will likely strike the southern part of the island on Oct. 4-5, the Joint Typhoon Warning Center said. Koinu's winds could reach 127 miles per hour, which would make it a Category 3 major storm on the five-step, Saffir-Simpson scale. It will then go on to strike China's coastline possibly near Shanwei and Shantou, China, however a larger area including Hong Kong is still under threat.

Europe: Autumnal heat will persist across much of continental Europe this week, with Madrid exceeding a maximum of 30C (86F) until Saturday, while Paris, Berlin and London will also be unseasonably warm, Maxar Technologies said in a daily note.