"It's a mess. The devastation is extensive," said Amy Boyle of the city's Chamber of Commerce. "There's lots of debris and its very toxic -- there are concerns about what was in the water," she said.

The rain-fed flood waters that roared over levees and through sandbagged barriers have created a multibillion-dollar disaster in Iowa and other Midwestern states.

Flood water may carry sewage, chemicals, farm waste, and dead animals, contaminating everything it touches.

Local flooding of this magnitude last occurred in the 1920s, when the population was much smaller than Cedar Rapids' current 120,000.

Hundreds of city blocks inundated last week by the swollen Cedar River may have to be leveled, including scores of downtown office buildings -- and concerns were raised about the city's proximity the river.

"We are seeing a lot of collapsed foundations in areas closest to the river," said Dave Koch of the fire department.

"Everthing is ... trashed," said John Tursi, director of the Boys and Girls Club. "There was grime and a sludge all over the floor and walls. There's still three feet (1 metre) of water in the gymnasium."

Among several museums and churches in Cedar Rapids hit by the flood was the Mother Mosque of America, where Imam Taha Tawil noted many faiths were affected: "Flood is like death ... it doesn't distinguish."

Business owners plugged dehumidifiers into portable generators and spread sand to dry out. Downtown Cedar Rapids lacked power because underground electrical vaults refilled with water as quickly as they were pumped out.

Iowans who rely on water from wells were advised to have them decontaminated. They also were told to get rid of tainted sandbags.

HUGE BUSINESS LOSSES

Five deaths in Iowa were blamed on the flooding or storms that began three weeks ago. But the damage to homes and infrastructure will take time to assess.

Iowa's governor asked for the federal government's help to repair widespread damage to railroad lines, bridges, highways, and other vital infrastructure such as water systems, utility grids and levees.

Huge business losses have mounted from missed rail and truck deliveries, idled barges, closed plants and shutdown factories. Agriculture, Iowa's biggest industry, has been among the biggest losers, with replanting of crops unlikely so late in the growing season and livestock losses seen high.

The farm losses, which have driven up corn prices and other commodities to or near record highs, may be long-term.

"I'm worried about how much damage has been done to the soil from lost nutrients and nitrogen," said Chip Flory of the Iowa-based Professional Farmers of America, a trade group.

On Main Street in Burlington, pumps shot a stream of flood water out of the aptly named Two Rivers Trust and Bank.

"I turned on my pump to get rid of the water and that wasn't enough. So I went and spent US$200 on a second one -- together they seem to be handling the job," said Christina Carle, who was pumping water from her Burlington home's basement.

Though flooding swirled through the University of Iowa campus in Iowa City, the school did not cancel fall classes.

"Now, exactly where we will put every one of those classes, we don't have that nailed down yet," University President Sally Mason said.

(Additional reporting by Kay Henderson in Des Moines, Nick Carey in Burlington, Sam Nelson in Chicago; writing by Andrew Stern; Editing by Peter Bohan and Vicki Allen)