ST. LOUIS — The gentle whir of passing barges is as much a part of life in St. Louis as the Gateway Arch and the Cardinals, a constant, almost soothing backdrop to a community intricately intertwined with the Mississippi River.

But next month, those barges packing such necessities as coal, farm products and petroleum could instead be parked along the river’s banks. The stubborn drought that has gripped the Midwest for much of the year has left the Mighty Mississippi critically low — and it will get even lower if the Army Corps of Engineers presses ahead with plans to reduce the flow from a Missouri River dam.

Mississippi River interests fear the reduced flow will force a halt to barge traffic at the river’s midpoint. They warn the economic fallout will be enormous, potentially forcing job cuts, raising fuel costs and pinching the nation’s food supply.

“This could be a major, major impact at crisis level,” said Debra Colbert, senior vice president of the Waterways Council, a public policy organization representing ports and shipping companies. “It is an economic crisis that is going to ripple across the nation at a time when we’re trying to focus on recovery.”

At issue is a plan by the corps to significantly reduce the amount of water released from the Gavins Point Dam near Yankton, S.D., a move to conserve water in the upper Missouri River basin also stung by the drought. The outflow, currently at 36,500 cubic feet per second, is expected to be cut to 12,000 cubic feet per second over several days, starting Friday.

The Missouri flows gently into the Mississippi around a bend just north of St. Louis. From there, about 60 percent of the Mississippi River water typically comes from the Missouri. This year, because of the drought, the Mississippi is even more reliant on Missouri River water — 78 percent of the Mississippi River at St. Louis is water that originated from the Missouri.

The Mississippi is so low there now that if it drops another 5 feet, barge traffic may shut down from St. Louis to the confluence of the Ohio River at Cairo, Ill., perhaps as soon as early December. Barges already are required to carry lighter loads.

Major Gen. John Peabody, commander of the Mississippi Valley Division of the corps, said the reduced Missouri River flow will remove 2-3 feet of depth of the Mississippi at St. Louis. To help offset that, he has authorized an emergency release of water from an upper Mississippi River reservoir in Minnesota. But that will add just 3-6 inches of depth at St. Louis.