CHICAGO (Reuters) - The swollen Mississippi River has flowed over the top of 19 levees in Missouri, Iowa and Illinois, and another 29 levees are at risk, the U.S. Army Corps of Engineers said on Wednesday.

The river overtopped at least nine levees overnight as water levels rose in the Midwest’s worst flooding in 15 years. The river was cresting in Burlington, Iowa, but has yet to reach its peak in many areas where the levees have already failed.

The compromised levees stretch from Dubuque, Iowa, to St. Louis and protect hundreds of thousands of acres of homes and farmland.

“We basically have about three dozen levee systems we’re concerned about overtopping as the river continues to rise,” said Ron Fournier, spokesman for the Corps’ Rock Island District, which had 11 of the 19 levees overtopped.

The 11 levees in the Rock Island District were protecting 68,000 acres, according to a map from the Corps of Engineers. The eight levees north of St. Louis protect 2,200 people and about 40,000 acres of agricultural land.

Once the river flows over the levee, it usually erodes the levee from the other side, causing a breach.

The levees in New Orleans broke during Hurricane Katrina in 2005, causing catastrophic flooding.