Sandbagging was under way in Burlington, a key rail hub, to build the city's levee system and protect it from the river; 350 people had been evacuated.
Two more deaths were reported, bringing the state's death toll from flooding to five. A 35-year-old man apparently drowned in Iowa River floodwaters near Wapello, and a woman was killed near New London when her stopped car was hit by a National Guard bus involved in flood duty.
"It's likely that we will see major and serious flooding on every part of the southeastern border of our state from New Boston and down," Gov. Chet Culver said. "We are taking precautionary steps, we are evacuating where necessary, but that is going to be the next round here."
Elsewhere in the soaked Midwest, National Guard soldiers hoped to fill about 500,000 sandbags by Monday to fortify levees along a 15-mile stretch of the Mississippi River near Quincy, Ill., and flood waters began to recede in parts of western Michigan.
The Iowa River's crest arrived early and lower than expected, possibly because of a number of levee breaches downstream that opened the channel, the National Weather Service said. Gov. Chet Culver called word of Iowa City's crest "a little bit of good news," but cautioned that the situation was still precarious.
One indication that the water levels were receding was the site of pavement on the Park Street Bridge in Iowa City, reports CBS News correspondent Hari Sreenivasan, who says it is the first time in four days that the road on the bridge is visible.
President Bush will visit the Midwest on Thursday to inspect flood damage, the White House said Monday as the president wrapped up a weeklong trip in Europe. White House press secretary Dana Perino said the places the president would visit had not been chosen.
Iowa City evacuated 5,000 people on Sunday, and 400 homes had suffered significant damage. But the river was expected to begin receding Monday night as the threat of new flooding flowed toward southeast Iowa.
"We made it through another day without any major incident and we feel fortunate for that," city manager Michael Lombardo said.
The University of Iowa reported no new damage overnight after floodwaters hit 16 buildings through the weekend. The school was working to restore power to buildings on the east side of the river.
Hundreds of homes were evacuated near the river Sunday, though it wasn't immediately clear how many suffered damage. More than a dozen buildings on the University of Iowa campus had taken on water, but school officials said they believed others were protected.
Early Monday, more than 38,000 residents in 26 Iowa communities had been evacuated from their homes, said Kevin Baskins of the state Emergency Operations Center. Most of those - 25,000 - were in Cedar Rapids, and another 5,000 in Iowa City, he said.
Eight people were pulled Sunday from the flooded Des Moines River in Ottumwa after their boat capsized, police Chief Jim Clark said. The boaters were exhausted, cold and showing some confusion. Four were being treated for hypothermia, Clark said.
On Monday, the river was at more than 20 feet - double the flood stage.
Sandbagging was under way in Ottumwa to protect the city's water treatment plant.
Also on the Mississippi River, the Army Corps of Engineers said Lock 12 at Bellevue, south of Dubuque, was reopened to river traffic on Sunday. But locks 13-25 remained closed, making 281 miles of the Mississippi from Winfield, Mo., to Fulton, Ill., inaccessible to commercial river traffic.
About 30 inmates from the Iowa State Penitentiary helped to sandbag in Burlington, a city of about 27,000. Already the city's four-story Memorial Auditorium was surrounded by water and some evacuations were under way.
In Iowa City, a town of about 60,000 where the Iowa River bisects both the school and the town, residents were cheered by the lower crest.
Donna Dubberke, a meteorologist with the National Weather Service in Davenport, said one reason that Iowa City's troubles may have eased was levee bursts down the river.
"Downstream there are some levees that have broken and we believe that some of that water is able to go off in those areas so that just provides a little more storage," Dubberke said.
The University of Iowa said 16 buildings had been flooded, including one designed by acclaimed architect Frank O. Gehry. Some buildings have as much as 8 feet of water inside.
"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."
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.
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 Monday 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.
Culver said cities big and small were getting adequate support in their efforts to survive the flooding.
"While we are having challenges in our urban centers we have multiple ongoing battles in the smaller communities," he said. "And we are doing just as much to help those rural, more remote areas of the state."
The threat to southeast Iowa was already taking shape, though the Mississippi River is days from cresting. State officials girded for serious flooding threats, sending 500 National Guard troops to Burlington.
More than 400 members of the Illinois Army National Guard were activated to assist with sandbagging efforts in Quincy. About 100 miles up the river in Keithsburg, a community of about 700 residents, water sat as high as 3 or 4 feet, said George Askew, an alderman. Multiple levee breaks prompted voluntary weekend evacuations.
"We're just biding the raising of the water and helping people who have to get their stuff out," Askew said.
The National Weather Service said the river was expected to crest there Tuesday just above 25 feet. Flood stage in the area is 14 feet.
The Iowa River breached levees in the town of Columbus Junction on Saturday evening, leaving much of the downtown, including a medical center, senior center, water plant and a couple dozen other businesses, under about 10 feet of water.
"So we ended up losing the battle, but there are a lot of good things that come out of an effort like that," said Mayor Dan Wilson. "The community spirit has been phenomenal."
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.
Meanwhile, flood waters receded in parts of western Michigan as the state tried to recover from a second straight weekend of severe weather.
The latest flooding followed rain that totaled 11 inches in less than 12 hours Thursday and Friday near Scottville, east of Ludington. The Pere Marquette River that enters Lake Michigan at Ludington in the western Lower Peninsula receded to 4.87 feet over flood stage Sunday afternoon, according to the National Weather Service.
About 29 roads in Mason County remained closed Sunday because of flooding. A sewage main that served about 90 percent of Ludington broke as a result of the rains, and repairs were completed Sunday afternoon. Drinking water in the city of 8,400 was safe, the officials said.