United States

By Alex Sosnowski, Expert Senior Meteorologist

August 23, 2012; 4:01 AM

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Near Vicksburg, Miss., water levels on the Mississippi River continue to fall as rocks normally submerged are exposed, Aug. 6, 2012. In 2011, the Mississippi River was overflowing near Vicksburg. (AP Photo/Robert Ray)

Plunging river levels along the Mississippi River are causing serious issues for barge traffic. The U.S. Coast Guard closed 11 miles of the river near Greenville, Miss., Monday. Almost 100 vessels are stuck waiting for the river to be dredged before they can finish their trip, according to Reuters.

Falling river levels are not uncommon during the summer months in the central and eastern United States. However, the historic drought over much of the middle of the nation has the mighty Mississippi running well below normal, the lowest levels since 1988. Since little rainwater is flowing into the Mississippi in the drought-stricken Midwest, it is affecting the water levels downstream.

Very low water levels have exposed shoals, potentially putting river traffic at risk for running aground.

The area of river closed Monday by the Coast Guard has been closed on and off since Aug. 12, when a barge ran aground, CNN reported. Some docking locations are becoming too shallow to remove cargo easily.

The problems will continue through the autumn, unless widespread and regular rain comes. On average, river levels and water tables reach their lowest point during the autumn, barring intervention of tropical weather systems.

"At the low water reference point of minus 3.5 feet, a safety zone is established in the navigation channel and some restrictions by the United States Coast Guard may be put in place," St. Louis Army Corps of Engineers Public Affairs Chief Mike Peterson said in July. "Officials will continue to patrol the river and may undertake dredging operations as necessary to keep channels and ports open."

The river level at St. Louis is forecast to fluctuate between 0.0 and -1.0 feet through much of the balance of August, but could dip lower to critical levels moving into the autumn. Negative readings occur on some of the gauges, because the river bottom has changed since measuring equipment was first put in place.

Due to the low river levels, barges operating in open areas of the Mississippi will continue to voluntarily carry lighter loads in attempts to avoid running aground. The lighter loads mean less profit for the barge companies, while some cargo may be shipped by more expensive means such as by truck or rail.

This story was originally published on Thursday, July 5, 2012 and has been updated. Content contributed by AccuWeather staff writer Grace Muller.