COLLINSVILLE, Ill. (AP) — Work to improve dozens of miles of earthen Mississippi River levees in southwestern Illinois may take several months longer than expected but won't dramatically affect the estimated $161 million cost, an overseer of the project said.

Les Sterman, the Southwestern Illinois Flood Prevention District Council's chief supervisor, said construction on the 64 miles of levees protecting a swath of land known as American Bottoms levees largely will be completed by the second quarter of 2015, The St. Louis Post-Dispatch reported Wednesday. Earlier estimates had anticipated that work would be done by the end of 2014.

Sterman attributed the delay to taking longer than anticipated to resolve the Army Corps of Engineers' concerns about a key element of the levee design. However, he said he believes it won't keep officials from securing 100-year certifications for the levees from Alton south to Columbia by the end of 2015.