Flooded Midwest braces for more rain

DES MOINES, Iowa (Reuters) - Rising rivers and swollen reservoirs caused severe flooding across the U.S. Midwest on Tuesday as residents in the region braced for yet another drenching.

Levees were breached or overtopped, sending flood waters coursing into some small towns in Iowa, Illinois, Indiana and Wisconsin. The National Weather Service forecast another round of thunderstorms coming from the northern plains on Wednesday.

In Des Moines, residents were warned that water would be released from a bulging reservoir into the Des Moines River, which bisects the city. All but one bridge over the river was closed.

Barack Obama, the presumed Democratic presidential nominee, canceled a planned campaign trip on Wednesday to Cedar Rapids, Iowa, so as not to divert state resources away from the unfolding disaster.

Levees failed along the Wabash and Embarras rivers in eastern Illinois, forcing dozens of people out of their homes.

Traffic was blocked by submerged roads and highways in some areas.

A bridge over the Mississippi River at Dubuque, Iowa, that was struck by runaway river barges was reopened, though authorities said flooding may force the closure of an upper section of the vital waterway.

"There's widespread damage, there's a lot of water where it shouldn't be, there are a lot of homes that have been damaged or destroyed," said John Erickson, a spokesman in Indiana for the U.S. Department of Homeland Security.

Three men have drowned in Indiana's flood waters since the weekend, when up to 10 inches of rain pummeled areas already soggy from heavy spring rains.

Indiana was suffering its worst flooding since the 19th century, Gov. Mitch Daniels said.

National Guardsmen and prisoners were helping to lay sandbags to raise levees along the cresting White River and other waterways in Indiana.

In some parts of the Midwest, the one-day respite from rains allowed the waters to recede. But governors in Minnesota, Illinois and Iowa issued disaster declarations for several counties, adding to broad swathes of Wisconsin and Indiana already under such declarations.

The prolonged Midwest rains and flooding led the U.S. Agriculture Department on Monday to trim 3 percent from the predicted U.S. corn crop this year, a rare downgrade so early in the growing season. Iowa and Illinois alone usually produce one-third of all U.S. corn and soybeans.

The crop losses at a time of urgent demand for food and fuel pushed corn prices at the Chicago Mercantile Exchange on Tuesday to a new record above $7 a bushel.

In southern Wisconsin, the summer tourist season will absorb a blow, with popular resorts on Lake Delton likely left high and dry. The man-made lake emptied on Monday when water from the rain-swollen lake forged a new path to the Wisconsin River, sweeping away a number of vacant homes with it.

(Writing by Andrew Stern; Editing by Peter Bohan and Eric Beech)