ST. LOUIS (AP) — Efforts taken to keep a crucial stretch of the drought-starved Mississippi River open to barge traffic should be sufficient to avert a shipping shutdown that the industry fears is imminent, Army Corps of Engineers and Coast Guard officials said Friday.

The corps said crews in recent weeks have made "fantastic" progress clearing treacherous bedrock from a channel about 150 miles south of St. Louis near Thebes, Ill. — the portion of the river that has grown especially worrisome to barge operators moving an array of cargo to northern states and south to the Gulf of Mexico.

Shipping groups warned this week that the waterway there could drop to a point — 3 feet on the river gauge — in which barge weight restrictions would have to be further tightented, effectively halting shipping.

Drafts, or the portion of each barge that is submerged, already are limited to 9 feet in the middle Mississippi. If the river gauge gets to 3 feet at Thebes, the Coast Guard may be forced to limit drafts even further. Officials with the trade group say that if drafts are restricted to 8 feet or lower, many operators will stop shipping.

National Weather Service hydrologists, as of Friday, forecast that the river at Thebes could drop to the 3-feet mark by next Thursday and continue falling to 1 foot by the end of this month.

"The uncertainty of this deteriorating situation for the nation's shippers is having as much of an impact as the lack of water itself," said Michael Toohey, president and chief executive of the Waterways Council Inc., which along with the American Waterways Operators group considers the situation dire.

Coast Guard Lt. Colin Fogarty said Friday it's possible that new draft restrictions may be considered by the middle of the month, but he believes the Army Corps' progress near Thebes and its overall stewardship of the river should make that unlikely.

As the barge industry submits, "we are absolutely facing very historic drought conditions," Fogarty said. "But this is a long-term campaign, and we've won many of the battles. We all want to have the deepest, safest channel, and right now we're accomplishing that."

The corps echoed that sentiment.

"We believe we will deepen the channel ahead of the worst-case river stage scenario, and I remain confident that navigation will continue," Maj. Gen. John Peabody, commander of the Army Corps' Mississippi Valley division, said in a statement this week.

"Rumors of a river closure have been greatly exaggerated," Mike Petersen, an Army Corps spokesman in St. Louis, told The Associated Press. "We're all working for the same thing — keeping the river open."

Addressing the river — specifically at Thebes — has been a headache for the corps for months as the nation's worst drought in decades stubbornly persists.

The depth of the Mississippi is regulated by dams north of St. Louis, and the depth increases south of Cairo, Ill., where the Ohio River converges. But the roughly 180-mile stretch from St. Louis to Cairo is approaching record lows. Experts say that if barges stop moving, billions of dollars of shipments of essentials such as corn, grain, coal and petroleum could be affected.

The trade groups renewed their call for presidential action requiring the Army Corps to increase the flow of water from an upper Missouri River dam in South Dakota. The corps cut the flow by two-thirds in November because of drought conditions in that region, reducing the amount of Missouri River water flowing into the Mississippi.

To compensate, the corps rushed in contractors last month to clear an estimated 890 cubic yards of limestone from the river bottom near Thebes — work that Petersen said has been "working fantastically" and should be completed by the end of January, perhaps sooner.

During that work, barge traffic at that stretch has been limited to an eight-hour window each day, causing bottlenecks of up to 20 vessels and 400 barges. The Coast Guard says more than 490 vessels still have made their way through, as of Thursday carrying 22,500 tons of cargo that's enough to fill the equivalent of 425,000 tractor-trailers.

The corps also strategically has released water from at least two Midwest lakes — Iowa's Red Rock Lake and southern Illinois' Carlyle Lake, the latter recently accounting for two 6-inch rises in the Mississippi.

Such releases won't impact the lakes environmentally or recreationally, Petersen said, noting that the corps routinely releases water from Carlyle into the Kaskaskia River that ultimately flows into the Mississippi.

"We judiciously use it," he said. "It's just one of our tools."

While crediting the Army Corps for having done everything it can, American Waterways Operators' Lynn Muench said Friday that such efforts don't "get us out of the woods" — something she said could happen if President Barack Obama's administration intervenes to release more water from the Missouri River. Now given the uncertainty, she said, some shippers already have lessened their barge loads in anticipation that more draft restrictions loom.

"It's still a mess," she said.