ST. LOUIS (AP) — Barge operators along a key stretch of the Mississippi River braced Monday for months of restricted shipping as crews prepared to begin blasting large rock formations that are impeding navigation on the drought-plagued waterway.

Contractors from Iowa and Ohio could begin drilling holes into the troublesome Mississippi River bedrock south of St. Louis and detonating explosives inserted inside as early as Tuesday, the Army Corps of Engineers said. They expect to remove enough rock to fill about 50 dump trucks, possibly more.

The demolition of the massive formations near Thebes, Ill., coincides with an unusual move by the agency to release water from a southern Illinois lake, adding a few inches of depth to a river that is getting lower by the day — largely because of the lingering effects of the nation's worst drought in decades.

The corps said a six-mile stretch of the river will be closed to shipping starting Tuesday from 6 a.m. to 10 p.m. to allow for the safe use of the explosives. Barges seeking passage will have to line up and wait for an eight-hour window when that stretch will be open, with the Coast Guard essentially acting as a flagman, letting barges through in one direction, then the other.

The project was initially to have begun in February but was expedited at the behest of U.S. lawmakers from Mississippi River states. Mike Petersen, a corps spokesman in St. Louis, said the agency was confident it could complete the project by the end of March.

The rock being removed typically would be beneath sand on the river bottom but has been exposed by the corps' dredging efforts to keep the channel open.

On Saturday, the corps began releasing water from Carlyle Lake into the Mississippi, saying the additional water will provide 6 inches of depth by Christmas Eve, enabling barge traffic to safely pass the rock formations. Gen. John Peabody, the corps' Mississippi Valley Division commander, said the "inches make a difference."

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., fanning concerns among barge operators that river use soon may be dramatically restricted, if it is not completely shut down. The problem worsened last month when the corps cut the outflow from an upper Missouri River dam by two-thirds, meaning far less water from the Missouri River flows into the Mississippi.

River industry trade group said the rock pinnacle removal and extra water from Carlyle Lake aren't enough.

"The release of a modest amount of water from Missouri River reservoirs during the time this rock pinnacle work occurs remains essential to allowing the continued movement of our nation's basic commodities, especially during this critical export season," said Michael J. Toohey, president and CEO of Waterways Council Inc. Continued...