IOWA CITY - A week's work of frantic sandbagging by students, professors and the National Guard couldn't spare this bucolic college town from the surging Iowa River, which has swamped more than a dozen campus buildings and forced the evacuation Sunday of hundreds of nearby homes.

The swollen river, which bisects this city of about 60,000 residents, was topping out at about 31.5 feet - a foot and a half below earlier predictions. But it still posed a lingering threat, and wasn't expected to begin receding until Monday night.

"I'm focused on what we can save," University of Iowa President Sally Mason said as she toured her stricken campus. "We'll deal with this when we get past the crisis. We're not past the crisis yet."

The university said 16 buildings had been flooded, including one designed by acclaimed architect Frank O. Gehry, and said others were at risk.

Iowa City Mayor Regenia Bailey said 500 to 600 homes were ordered to evacuate and hundreds of others were under a voluntary evacuation order through the morning. The city had no estimate of the number of homes that had actually flooded.

Bailey said homeowners will not be allowed back until the city determines it's safe.

Gov. Chet Culver said it was "a little bit of good news" that the river had crested, but cautioned that the situation was still precarious.

"Just because a river crests does not mean it's not a serious situation," he said. "You're still talking about a very, very dangerous public safety threat."

Elsewhere, state officials girded for serious flooding threats in Burlington and southeast Iowa including Fort Madison and Keokuk. Officials said 500 National Guard troops had already been sent to Burlington, a Mississippi River town of about 27,000, and some people were being evacuated.

Culver said the southeastern part of the state was likely to "see major and serious flooding on every part of the southeastern border of our state from New Boston and down."

In Cedar Rapids - where flooding had forced the evacuation of about 24,000 people from their homes - residents waited hours to get their first up-close look since flooding hammered most of the city earlier this week.

Some grew angry after long waits to pass through checkpoints. Cedar Rapids officials also were inspecting homes for possible electrical and structural hazards.

"It's stupid," said Vince Fiala, who said he waited for hours before police allowed him to walk five blocks to his house. "People are down on their knees and they're kicking them in the teeth."

The city's municipal water system was back to 50 percent of capacity Sunday, a big victory after three of the city's four drinking water collection wells were contaminated by murky, petroleum-laden floodwater. That contamination had left only about 15 million gallons a day for the city of more than 120,000 and the suburbs that depend on its water system.

After much of the University of Iowa's Arts Campus flooded in 1993, raised walkways were installed that doubled as berms. But those were quickly overwhelmed by the Iowa River's rising waters.

Standing beside the grayish water surrounding the limestone and stainless steel Iowa Advanced Technologies Laboratories, designed by Gehry, Mason choked up.

"I got tears in my eyes when I saw what was happening here," she said.

Across the river, Art Building West was surrounded by a lagoon of murky water. Designed by Steve Holl, it was one of only 11 buildings in the world recognized last year by the American Institute of Architects, said Rod Lehnertz, director of campus and facilities planning.

The damage would have been worse had it not been for the Herculean efforts of students, faculty, National Guard troops and others who swarmed the campus over several days to erect miles of sandbag walls, some as high as 9 feet.

On Saturday alone, volunteers filled and installed more than 100,000 sandbags, Lehnertz said.

Lehnertz was confident that buildings that hadn't flooded by Sunday were well-protected. He said the most pressing issue was flooding in the six miles of underground tunnels that feed steam to campus buildings for power. Workers pumped water from the tunnels into the streets and down toward the river.

Some buildings at the Arts Campus on the river's west bank had as much as 8 feet of water inside.

All elective and non-emergency procedures were canceled at the university hospital, and non-critical patients were discharged, Mason said. Nurses were brought in from elsewhere to ensure all emergency shifts would be covered.

Bruce Brown, 64, a retired radiology professor at University of Iowa Hospitals and Clinics, spent three days filling sandbags on the east bank. But picturesque brick Danforth Chapel, where his daughter was married, flooded anyway.

"When I think about moving rare books from the bottom of the library, I weep," he said. But then he joked about pulling sandbag duty with a hulking Hawkeye football player.

"I weigh 129, he weighs about 300 pounds," he said. "He would ship these thing that were like dead bodies to me. But that was fine. We worked together and got it done."

Elsewhere in the Midwest, hundreds of members of the Illinois National Guard headed to communities along the swollen Mississippi River on Sunday for sandbagging duty while emergency management officials eyed rain-swollen rivers across the state.

Two levees broke Saturday near the Mississippi River town of Keithsburg, Ill., flooding the town of 700 residents about 35 miles southwest of Moline. The National Weather Service said the Mississippi would crest Tuesday morning near Keithsburg at 25.1 feet. Flood stage in the area is 14 feet. Rising water threatening approaches also prompted Illinois officials to close a Mississippi River bridge at Quincy.

Associated Press writers Melanie S. Welte in Des Moines, Jim Salter in Iowa City Maria Sudekum Fisher in Columbus Junction, Iowa, Don Babwin in Chicago and Charles Babington in Quincy, Ill., contributed to this report.