IOWA CITY, IOWA - 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 was not expected to begin receding until tonight.

"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 flooded, including one designed by acclaimed architect Frank O. Gehry, and others were at risk.

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

Bailey said homeowners will not be allowed back until the city determines that it is 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.

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

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

The city's 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 petroleum-laden floodwater. That contamination 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.

Students, faculty, National Guard troops and others swarmed the campus over several days to erect miles of sandbag walls, some as tall as 9 feet.