U.S. Coast Guard and Army Corps of Engineers inspectors say the barges that broke loose last week on the Illinois River damaged the dam near Marseilles.
Officials on Monday said the inspectors found three gates and anchorage systems at the dam broken.
They said the damage won't cause additional flooding risk to downstream communities. However, a decrease in water depth of the pool between Marseilles Lock and Dam and the Dresden Island Lock and Dam could lead to a decrease in navigation depth of the Illinois River and impact its usage.
Mike Cox of the corps of engineers says the dam is considered critical to Illinois River operations.
The mishap occurred when river currents resulting from last week's heavy rains redirected the barges toward the dam. Three of the seven barges sunk.