Oakville, Iowa ? The floodwaters that deluged much of Iowa have done more than knock out drinking water and destroy homes. They have also spread a noxious brew of sewage, farm chemicals and fuel that could sicken anyone who wades in.

On Monday, Bob Lanz used a 22-foot aluminum flatboat to navigate through downtown Oakville, where water reeked of pig feces and diesel fuel.

“You can hardly stand it,” Lanz said as he surveyed what remained of his family’s hog farm. “It’s strong.”

LeRoy Lippert, chairman of emergency management and homeland security in nearby Des Moines County, warned people to avoid the floodwaters: “If you drink this water and live, tell me about it. You have no idea. It is very, very wise to stay out of it. It’s as dangerous as anything.”

As some of Iowa’s flooded towns began cleaning up Monday, others braced for new flooding risks, particularly in southeastern Iowa along the Mississippi River.

The federal government predicts that 27 levees could potentially overflow along the Mississippi River if the weather forecast is on the mark and a massive sandbagging effort fails to raise the level of the levees, according to a map obtained Monday by The Associated Press.

Officials are placing millions of sandbags on top of the levees along the river in Illinois, Iowa and Missouri to prevent overflowing.

In Des Moines County, where the Mississippi was expected to crest Wednesday, authorities had asked for a half-million sandbags.

“We have just begun to fight,” Gov. Chet Culver said. Two more deaths were reported Monday, including a woman whose car was hit by a National Guard truck, bringing the state’s death toll to five.

Also Monday, the American Red Cross said its disaster relief fund has been completely spent, and the agency is borrowing money to help flood victims throughout the Midwest.

In the college town of Iowa City, damage appeared limited. Some 400 homes took on water Sunday, and 16 University of Iowa buildings sustained some flood damage over the weekend. But the town’s levees were holding and the Iowa River was falling.

In northeast Missouri communities along the Mississippi, armies of Mennonites and Amish worked sandbag lines with convicted felons, college students and other volunteers in a race to beat the rising river.

The very wide Mississippi was forecast to crest in the area by mid- to late-week.

“Today is our critical day, we need to get it done,” said Monica Heaton, spokeswoman for Canton, Mo.’s emergency operations center.