ST. LOUIS — Shippers who have idled towboats and lightened barge loads as the Mississippi River shrinks from drought credit the waterway’s stewards for averting their worst fear: a potentially crippling shutdown of the artery used to move everything from corn and grain to construction materials and petroleum.

Barge operators still are being squeezed financially because of restrictions on the waterway. But “the Army Corps of Engineers has done a great job of pulling rabbits out of their hat” by scrambling to rid one crucial river stretch of treacherous bedrock while strategically releasing water from lakes into the Mississippi to raise the river, said Rick Calhoun, president of Cargo Carriers, Cargill Inc.’s shipping arm with 1,300 barges.

“We believed it was an oncoming crisis, and by hook and by crook it hasn’t gotten as bad as we thought,” he added. “That’s great news.”

Barge industry trade groups had been critical of the corps, warning that the river would likely close because the agency was cutting the flow of the flow of the Missouri River into the Mississippi amid the worst U.S. drought in decades. The corps rebuffed the industry’s pleas that the flow from a South Dakota dam be restored, saying the pullback was needed to protect interests on the upper Missouri.

To compensate, the corps rushed in contractors in December — two months ahead of schedule —  to clear limestone from the Mississippi’s bottom near Thebes, Ill., where increasing shallowness made the jagged bedrock more precarious for vessels.

The corps and barge operators agree that the rock removal is working, though not without some inconvenience for shippers. Barge traffic at that stretch is now limited to an eight-hour window each day, causing bottlenecks and slowing transit times of cargo.

Shipping groups have warned that if the waterway there were to drop to a point in which barge weight restrictions were further tightened, shipping would effectively stop. Drafts, or the portion of each barge that is submerged, already are limited to 9 feet in the middle Mississippi, down from 12 feet. Trade group officials say that if drafts are restricted to 8 feet or lower, many operators will stop shipping.

While lessening cargo weight helps barges ride higher, shipping costs increase because more barges are required to move the cargo and tow boats go through more fuel because more trips become necessary.

The National Weather Service hydrological forecast as of Thursday showed that the river at Thebes — about 130 miles south of St. Louis — still would be 2 feet higher than the threshold for more possible barge restrictions as of Feb. 6, the latest date on the outlook.

Mike Petersen, a corps spokesman in St. Louis, said the river’s extremely low level at Thebes has allowed contractors using explosives and two dredging crews to rid rock pinnacles much faster than anticipated, adding roughly 3 feet of depth to the channel. “If there’s any silver lining with the low water, that’s it,” he said.

The corps also has released water from at least two Midwest lakes — Iowa’s Red Rock Lake and southern Illinois’ Carlyle Lake, the latter accounting for two 6-inch rises in the Mississippi that Petersen said “made a huge difference.”

“It truly is a battle of inches when the river is this low,” he said.

Barge operators hope that if the corps can keep the Mississippi passable for the next month or so, spring rains, snow melt off and the back-to-normal release from the Missouri could raise the Mississippi, erasing any lingering alarm about shipping.

The size of Cargo Carriers’ barges on the Mississippi is roughly half of what they typically would be, Calhoun said. Because of earlier concerns about the river’s passability, the Cargill arm loaded some northbound barges to only an 8-foot draft, knowing that for every foot of reduced draft 200 fewer tons — or 13 percent — gets shipped.  

Cargo Carriers also declined other business and cleared out some equipment north of St. Louis, fearing a river closure would trap those assets, Calhoun said.

“The good news is that it hasn’t gotten as bad,” Calhoun said.

At AEP River Operations, many of the company’s 3,100 barges and roughly 100 towboats were parked while the river was falling, said Marty Hettel, senior manager of bulk sales. The corps’ work at Thebes — and more-promising river gauge forecasts — prompted AEP to press idled vessels into action, giving the company as much as 350,000 tons of capacity in the next couple weeks.

Still, “it’s a hold-your-breath moment,” said Lynn Muench of the American Waterways Operators trade group. “We’re not out of the woods.”