U.S. Sen. Roy Blunt, R-Mo., and two river industry trade groups said Tuesday that the Army Corps of Engineers informed them that blasting could start next week, although it wasn't clear which day the work could start or how long it might take. The corps didn't respond to several messages seeking comment.

Removal of the rocks is an important step in keeping the river open to barge traffic. Months of drought have left water levels up to 20 feet below normal along a 180-mile stretch of the river from St. Louis to Cairo, Ill. The problem was made worse last month when the corps cut the outflow from an upper Missouri River dam by two-thirds — meaning far less Missouri River water flows into the Mississippi.

Officials with the trade groups American Waterways Operators and Waterways Council Inc. said expediting the rock removal will help, but they maintain that the corps also needs to restore some of the Missouri River flow.

"The release of sufficient water from Missouri River reservoirs during the time this rock pinnacle work takes place is essential to preserving a 9-foot channel on the Mississippi River that will sustain commercial navigation and the movement of our nation's critical commodities and exports," said Michael J. Toohey, president and CEO of Waterways Council Inc.

Blunt agreed.

"The corps is finally heeding my calls to expedite rock removal & help prevent a river crisis," Blunt wrote on Twitter. "Water releases from the MO River must be next."

The corps removed many rock pinnacles in the southern Illinois area more than two decades ago. Sonar wasn't as advanced in the late 1980s and new technology recently revealed formations they missed near the towns of Thebes, Ill., and Grand Tower, Ill.

The corps originally planned to hire contractors to get rid of those pinnacles starting in February. Army Assistant Secretary Jo-Ellen Darcy met with senators from Mississippi River states about two weeks ago, and at their request ordered the process expedited. Corps officials moved the timeline up, initially to early January, now to December.

The river depth on Tuesday was at about 12 feet in St. Louis. The U.S. Coast Guard has said that if it dips to around 9 feet, further restrictions on barges may become necessary. The National Weather Service has forecast that the river will drop to the 9-foot level late this month, barring significant rainfall.

The Coast Guard has said it does not expect to close the river. But Tom Allegretti, president and CEO of American Waterways Operators, said any additional restrictions on barges will leave the river "as good as closed."

Barges, normally allowed 12-foot drafts, are already restricted to 9-foot drafts because of the low water level. That means lighter and more frequent loads. If the restriction goes to 8 feet, some operators say they'll halt shipping.

The trade groups say a prolonged stoppage of barge traffic could have an economic impact reaching into the billions of dollars. Agricultural products, coal, petroleum and other goods rely on river shipping.

"This is still very much a crisis situation," said Ann McCulloch of American Waterways Operators.