The Mississippi River at Vicksburg stood about level this morning, though a rock spill clogged the navigation channel to barge traffic on Wednesday upriver near St. Louis.

Official readings showed the river at 1.57 feet at Vicksburg, unchanged since Wednesday. The gauge’s elevation above sea level is 46.23 feet, which means there’s alost 48 feet of water in the river.

The worst drought in decades has kept the river dramatically lower since late spring. Forecasts show the level dropping to 0.6 feet on the Vicksburg gauge by Oct. 16, a slightly higher outlook than earlier this month. The record low is minus 7 feet, set in 1940.

Cargo moved more slowly in August at the Port of Vicksburg, on the Yazoo Diversion Canal, off the main channel. A monthly report showed 18,378 tons of steel coil, corn screens and lumber were loaded, down more than 10,000 tons from July. Dredging at the port is expected to start around Sept. 30.

Repairs were expected to continue through today on Lock 27, north of St. Louis, which was closed Saturday after tons of rock spilled from a protection cell and blocked passage for nearly five dozen tugboats and more than 400 barges carrying everything from grains to coal to fertilizer and construction materials, the U.S. Coast Guard reported. Throughout the day, vessels were parked at ports up and down the river to save fuel.

Barge traffic was expected to slow near Vicksburg due to restrictions in place while the lock is repaired.

“It’ll just be slower until the queue is cleared up,” said New Orleans-based Coast Guard spokesman Petty Officer Ryan Tippets. Traffic moved this morning near the lock 10 vessels at a time, Tippets said.

Damage was on an unarmored part of the protection cell that barges don’t typically touch because it’s 15 to 20 feet under water. Due to low water, that part of the structure has stood exposed.

Roughly half of the nation’s farm exports pass through the lock, now closed at a time when Midwest growers are harvesting corn and soybeans.

The tonnage caught up in the traffic jam was enough to fill 2,400 railcars or 23,600 large tractor-trailers, the Coast Guard said.

“Imagine taking an eight-lane highway and reducing it to a four-lane one and having a massive traffic backup. That’s what we’re dealing with,” Coast Guard Lt. Colin Fogarty said. “It’s like trying to find a parking spot at the mall on Christmas Eve — chances are you’re going to have to park far away, and you may not want to go at all.”

At Greenville, the river was down slightly, to 8.5 feet, this morning. The river closed intermittently there in August when barges ran aground in low water.

Losses to the barge industry were estimated at $1 billion in 1988, the last time the river was this low. At St. Louis-based AEP River Operations, payloads have been reduced by an average of 25 percent, or about 1,500 tons, said Martin Hettel, senior manager for bulk sales.

A busy dredging by the Corps and contract vessels continued this week north of Vicksburg and near Lake Providence Harbor. The Corps-owned Jadwin and the contract Butcher were to work through Friday. The Corps’ Mat Sinking Unit worked south of Memphis this week.

The Associated Press contributed to this report.