The bleak news came as swollen rivers breached levees in the state capital, Des Moines, and in far western Illinois, leading to the evacuation of hundreds more homes.
Officials guess it will be four days before the Cedar River drops enough for workers to even begin pumping out water that has submerged at least 438 blocks, threatened the Cedar Rapids drinking water supply and forced the evacuation of a downtown hospital.
"We're estimating at least a couple of weeks before the flood levels get down right around flood stage and below," said Dustin Hinrichs of the Linn County emergency operations center.
The Cedar River crested Friday night at nearly 32 feet, 12 feet higher than the old record set in 1929. By Saturday morning the river level had dropped more than 2 feet and was continuing to fall about 2 inches an hour.
Officials increased their estimate of residents forced from their homes to 24,000, a figure based on the belief that at least 3,900 homes had been evacuated. Cedar Rapids has a population of about 120,000.
"It's a bit overwhelming ... " said the city's mayor pro-tem, Brian Fagan. "This is an endurance competition. We have to be patient. We have to be cooperative."
Even as the river slowly recedes, Cedar Rapids officials worried that the city's supply of fresh drinking water would run out.
Cedar Rapids has only one of 44 wells working, Fire Department spokesman Dave Koch told The Early Show. "Forty-three of them are under water and not working. We're only producing 25% of the water that we need. Unfortunately, we're still using more water than we're producing. So we're still asking residents, businesses and industry to severely cut back on water use."
The sole working well was being protected by sandbags and pumps powered by generators. Crews hoped to gain access to flooded wells Saturday to see if they could make repairs to get them back online.
But with every passing hour, the city's drinkable water level dropped as residents used more water than the well and supplemental sources from nearby towns could provide.
"We will deplete our supply in three to four days unless we get further reduction in use," said Pat Ball, the city's utilities director.
CBS News correspondent Hari Sreenivasan said it is expected to be four days before the streets of Cedar Rapids are visible again.
"It won't be until June 18 that we will be below what was predicted to be the crest, which what was the previous record," Cedar Rapids Mayor Kay Halloran told the CBS Early Show.
On Friday the full scope of the damage was becoming clear. At least 438 city blocks were under water, hospital patients in wheelchairs and stretchers were evacuated in the middle of the night, and officials said as many as 10,000 townspeople had been driven from their homes in this city of 120,000.
Sreenivasan reported on a new ferry service in southwest Cedar Rapids, where the tree-lined streets are now waterways. Boater Tony Iaillo helps homeowners salvage what they can.
"All my stuff's going to be ruined," one flood victim said. "My whole life."
Iaillo helps a woman retrieve her medication.
Some ignore the warnings of the filth and danger in the water and plow through anyway to recover what's most important to them - like one who rescued his pets. "We ain't going to let our dogs die," he said.
Preliminary damage estimates in Cedar Rapids reached $737 million, and city officials foresee a long recovery.
Just south of Cedar Rapids, in Iowa City, the Iowa River had caused major damage by Saturday even though the crest was at least two days away. The river is expected to reach 33 feet to 34 feet late Monday or early Tuesday, far above the 25-foot flood stage.
"This is our version of Katrina," Johnson County Emergency Management spokesman Mike Sullivan said. "This is the worst flooding we've ever seen - much worse than 1993," when much of the Midwest was hit by record flooding
At the University of Iowa, whose campus is bisected by the Iowa River, students and faculty joined with townspeople and members of the National Guard to fill thousands of sandbags in the area known as the Arts Campus. But it wasn't enough.
"We've pretty much just abandoned any effort to try and protect the Arts Campus because we are just overwhelmed by the amount of water," university spokesman Steve Parrott said. "It's just too unsafe."
Only one bridge connecting the east and west sides of downtown Iowa City remained open, and officials said it may have to be closed this weekend.
The flooding was blamed for at least two deaths in Iowa.
Since June 6, Iowa has gotten at least 8 inches of rain, following a wet spring that already had saturated the ground. As of Friday, nine rivers were at or above historic flood levels. More thunderstorms are possible in the Cedar Rapids area over the weekend, but next week is expected to be sunny and dry.
Gov. Chet Culver declared 83 of the state's 99 counties disaster areas, a designation that helps speed aid and opens the way for loans and grants.
The drenching has also severely damaged crops in America's No. 1 corn state and other parts of the Midwest at a time when corn prices are soaring. Dave Miller, a grain farmer and director of research for the Iowa Farm Bureau, estimated that up to 1.3 million acres of corn and 2 million acres of soy beans - about 20 percent of the state's overall grain crop - had been lost to flooding.
Levee Breached In Des Moines
About 100 miles to the west, Des Moines dealt with its first major flooding after a levee ruptured early Saturday, allowing water to pour out of the Des Moines River and into a small neighborhood north of downtown.
Authorities said 270 homes had been ordered evacuated Friday, and many other residents left the area voluntarily. Bill Stowe, the city's public works director, said he expected extensive damage to about 200 homes and 35 businesses in the neighborhood.
Des Moines city crews and National Guard members tried to build a temporary berm to try to stop the water, but authorities ordered the project abandoned by midmorning because they didn't expect it to hold.
Elsewhere, Illinois emergency authorities said a levee along the Mississippi River in far western Illinois burst Saturday morning and voluntary evacuations were under way in Keithsburg, a town of about 700 residents.
"The levee broke in two places," Keithsburg Alderman George Askew, 76, said of the town some 35 miles southwest of Moline. "We're getting under water."
There was flooding in about a third of the town, said Jennifer Hamerlinck, Mercer County's emergency manager.