Image credit: Rogelio V. Solis/AP Images

Experts who watch the Mississippi River say they haven't seen it this low since the 1940s.

These days, the river, which sometimes resembles a slow-motion interstate highway for barge traffic, has narrowed to one lane - where the water is the deepest.

Outside Memphis, Tenn., crews raced to remove a car from the river. It had been quietly sitting at the bottom for years but as the water level went down, it was suddenly blocking traffic.

River traffic was backed up for 11 miles tonight as vessels waited for a stretch of the river to be reopened.

Officials say the Mississippi River's water levels have gone down dramatically - from Illinois to Louisiana - because of drought conditions over the last several months.

Like a wreck on the road, a barge that was stuck in the mud blocked traffic as nearly 100 boats and barges waited to move.

The U.S. Army Corps of Engineers said it was dredging the river to keep water at least 9 feet deep - any less and authorities said they would be forced to close the river.

Frank Segree, captain of the U.S. Army Corps of Engineers' Dredge Hurley, said there had been some "close calls" with ships hitting the river's bottom.

The Mississippi is the nation's artery of commerce, where more than 500 tons of grain, coal and other goods are moved every year.

More than 400,000 U.S. jobs depend on the flow of river traffic, and each day that traffic on the river stops, the U.S. economy loses $300 million.