The rising Mississippi River broke through a levee Tuesday, forcing authorities to rescue about a half-dozen people by helicopter, boat and four-wheeler as floodwaters moved south into Illinois and Missouri.

But even as the water jeopardized scores of additional homes and businesses, officials said the damage could have been worse if the federal government had not taken steps to clear flood-prone land after historic floods in 1993.

On Tuesday, the flooding halted car travel over two bridges linking Illinois and Iowa and threatened to cover areas near tiny Gulfport with 10 feet of water.

"I'm not going back after this one," 83-year-old Lois Russell said as she watched water surround her house near Gulfport. It was the third time she had fled her home because of flooding since 1965.

"It was a good place to raise my seven kids," she said, crying. "I know I haven't lost anything that feels important because I have a big family."

The situation in Gulfport is one of many across the upper Midwest that prompted President George W. Bush on Tuesday to pledge housing help and other federal aid to victims, as well as federal aid to farmers and ranchers.

The president plans to visit flood-stricken Iowa on Thursday, where heavy rains have washed out millions of acres of prime farm and grazing lands, raising the likelihood of higher food prices.

White House spokesman Tony Fratto said that although it's too early to say what the exact impact will be, "it will certainly cause disruptions, in terms of the food supply coming from that region.

He will get a West Wing briefing from emergency chiefs on the swamping of parts of Iowa and Illinois by the rain-swollen Cedar, Iowa and Mississippi Rivers. Hundreds of homes have been damaged and tens of thousands of residents have been forced to evacuate.

Aides said the president got regular briefings during his European trip.

About 20 miles downriver of Gulfport, a railway bridge was closed to car traffic near the Iowa-Illinois line.

About 30 people were working to raise the tracks above floodwaters. Officials said railway traffic has not been disrupted.

A state official said there have been more than a half-dozen levee breaches in Illinois in the past week or so.

The federal government said up to 26 other levees along the Mississippi River could overflow in the coming days.

Most communities near the water in southeastern Iowa have already been sandbagging levees, and in some cases pumping water out of basements as it starts to flood in certain areas.

Through much of central Iowa on Tuesday, attention turned mainly toward cleanup efforts necessitated by the floodwaters, which have knocked out drinking water and destroyed homes.

The remaining floodwater has the potential to make people sick as sewage mixes with fuel, farm chemicals and anything else the water picks up.

LeRoy Lippert, chairman of emergency management and homeland security in Des Moines County, Iowa, warned people to avoid the floodwaters.

"If you drink this water and live, tell me about it," he said.

All manner of refuse could be seen floating down the Cedar River; 55-gallon drums labeled "corrosive," propane tanks, wooden fences and railroad ties.

In addition to the poison in the water, there are mosquitoes -- millions of them spawning in acres of standing water.

More than 36,000 residents in 26 Iowa towns were out of their homes Monday morning, with most of them from around Cedar Rapids.

A total of five deaths have been attributed to the floodwaters.