US Army engineers are dredging the dwindling Mississippi River 24/7 and battling seawater creeping upstream toward New Orleans' drinking water

• The Mississippi River is incredibly low for the second year in a row.
• This threatens both the country's international supply chain and national drinking water access.
• Authorities are battling against Mother Nature to try to keep the freshwater flowing. 

A long stretch of drought in the Midwest has caused the Mississippi River to drop to abnormally low levels. It's the second year in a row the river has dipped so low.

The low river threatens cargo ships that carry 60% of all grains produced in the US. It also jeopardizes access to drinking water for many Louisiana residents. 

In other words, it's a serious problem. 

"It is the most important working river on Earth," Colin Wellenkamp, the executive director of the Mississippi River Cities and Towns Initiative, said in a town meeting per the Associated Press.

Problem 1: supplies of corn, wheat, and soy are in peril

The Mississippi River is a crucial route for farmers trying to move their corn, wheat, and soy across the country, which is especially important right now because it's harvest season.

Shipping crops on the Mississippi River is ideal because it's low-cost, efficient, and can handle huge amounts of cargo at a time. Just 15 barges lashed together can carry as much cargo as about 1,000 trucks, the AP reported.  

But the river's low levels are causing delays. It's forcing barges to lighten their loads so they carry less cargo. It's also narrowing the river, causing barge backups, per the AP.

These delays have sent costs of cargo transport skyrocketing up 77% from the past three-year average, per the AP.

"Economically it's tough because you don't want to rule out one of the modes of transportation for exports," Lou Dell'Orco, chief of operations and readiness at the US Army Corps of Engineers St. Louis District, told Insider.

Keeping ships running

The absolute minimum that barges need to drift down the river is 9 feet deep and 300 feet wide. The first line of defense in keeping water levels up is vacuuming. 

USACE workers operate boats, called dredges, that slurp up debris from the river bed and sift through the material, sending the water back into the river and the flotsam to a disposal site. 

Dell'Orco said that right now the St.Louis district of USACE has two dredges running 24/7 in the St. Louis region, which is a crucial chokepoint for the river. The region brought in two more dredges from other districts to help out. 

Though it's normal to have some dredges operating 24/7 during this season, last year they had to mobilize far more dredges than normal to keep the river deep enough. This year looks like it will be more of the same, Dell'Orco said.

Right now, Dell'Orco said they're staying on top of the issue, and keeping the river running. But what they're all hoping for is rain.

"With this current hit it looks like we're OK beyond almost the middle of October. The goal is to keep looking until we can get the harvest out," he said.

Problem two: Louisiana's drinking water is at stake

An estimated 18 million people get their drinking water from the Mississippi. 

When the Mississippi river is low, its flow decreases. When its flow decreases, saltwater from the Gulf of Mexico begins to creep up into the river, which contaminates drinking water. 

Louisiana Gov. John Bel Edwards addressed a letter to President Joe Biden, asking for federal intervention to stymie the effects of the encroaching saltwater, which Biden approved on Wednesday.

The saltwater invasion has already affected farms, schools, and homes. For example, it's contaminated the drinking water of roughly 23,515 residents in Plaquemines Parish where residents are advised to only drink bottled water. 

Officials are supposed to bring in 15 million gallons of fresh water to treatment facilities in impacted areas, the AP reported. 

Edwards emphasized that in the coming months, this problem could continue to head up the river, threatening more populous areas, like New Orleans.

Slowing the saltwater's invasion

Matthew Roe, with the New Orleans district of USACE, told Insider that it's been working 24/7 since the 24th of September, trying to get ahead of the saltwater flow.

First, they're using dredging, with the same technique as the St. Louis location, just with fewer boats. They're using what they collect from the river bottom to help construct their second effort, sills. 

Sills are long bars that sit along the river bed and can block out water flow from one direction to raise the water levels. The engineers are focusing on building on top of a sill that they placed in July. 

Adding another 15-feet to the top of that structure will hopefully delay the northwards flow of saltwater by 10-15 days without impeding the flow of traffic, Roe said. 

These aren't permanent solutions, but they buy local communities precious time to prepare to find alternate drinking water sources, Roe added. 

"The sill is used to delay progression as it moves upriver to allow the state and local communities more time to coordinate their efforts for the residents in the area," he told Insider via email.

Though efforts are Herculean, every engineer was aware that the force they were up against was formidable. "At some point, like last year, if Mother Nature decides she's gonna win, she's got a perfect record," Dell'Orco said.