Iowa ? Rising rivers wiped out an Iowa railroad bridge Tuesday, flooded Illinois farmland and forced residents along the Mississippi River to prepare for what could be the worst flooding in 15 years.

In Cedar Falls, Iowa, officials were readying residents and downtown business owners to evacuate as the Cedar River threatened to spill over a levee. The river was expected to top the levee early today, prompting a mandatory evacuation of downtown, Mayor Jon Crews said.

In nearby Waterloo, fast-moving water swept away a railroad bridge used to transport tractors from a John Deere factory to Cedar Rapids. It also prompted the city to shut its downtown and close five bridges.

Levee breaks Tuesday in southeastern Illinois flooded 50 to 75 square miles of farmland along the Embarras River, forcing the evacuations homes northeast of Lawrenceville, said Lawrence County Sheriff Russell Adams. He said water was up to the roofs of some rural homes.