As many as 10,000 townspeople driven from their homes by the rain-swollen Cedar River took shelter at schools and hotels or moved in with relatives. As many as 3,000 homes have been evacuated, reports CBS News correspondent Dean Reynolds, and the river is expected to crest at nearly 32 feet Friday night.
About 100 miles to the west, the Des Moines River threatened to spill over the levees into downtown Des Moines, prompting officials in Iowa's biggest city to urge people in low-lying areas to clear out by Friday evening. The river was expected to crest a couple of hours later.
"We are perilously close to topping the levees," said Bill Stowe, public works director in the Iowa capital, population 190,000. He added: "It's time to step out of harm's way."
Concerns were greatest in the east, reports Reynolds, where Columbus Junction is braced for a deluge with an improvised levee built in less than two days that residents hope will keep the Iowa River at bay.
"We're trying to create what I call a bathtub," said Hal Prior, Columbus Junction City Councilman. "Except that you don't want water in the bathtub, you want to keep it out of the tub."
Reynolds reports another town is also bracing itself for possible flodding - Oakville, population 439.
In town, men, women, children and even a few prisoners put their shoulders into the fight against the tide, adding heft and height to the levee for mile after mile.
"The attitude's great," said K.C. Jackson. "Everybody's working hard to get accomplished what we need to get accomplished."
The flooding has been blamed for at least two deaths in Iowa: a driver was killed in an accident on a road under water, and a farmer who went out to check his property was swept away.
Since June 6, Iowa has gotten at least 8 inches of rain. That came after a wet spring that left the ground saturated. 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.
In Cedar Rapids, the engorged river flowed freely through downtown. At least 438 city blocks were under water, and in some neighborhoods the water was 8 feet high. Hundreds of cars were submerged, with only their antennas poking up through the water. Plastic toys bobbed in front of homes.
For decades, Cedar Rapids escaped any major, widespread flooding, even during the Midwest deluge of 1993, and many people had grown confident that rising water would pose no danger to their city. The flood this time didn't just break records; it shattered them.
The Cedar River was expected to crest Friday night at nearly 32 feet, an astonishing 12 feet higher than the old record, set in 1929.
Flooding left 2 inches of water in the emergency room at Mercy Medical Center in Cedar Rapids on Thursday night, and water spilling into the lower levels threatened to knock out the hospital's emergency generator.
A total of 176 patients - some of them frail, about 30 of them from a nursing home at the medical center - were moved to other hospitals in an all-night operation that was not completed until daybreak.
"Those poor people. They looked half-terrified and half-thankful that they had someplace to go where they could finally rest and be cared for," said Sonya Thornton, a technician at St. Luke's Hospital in Cedar Rapids, where many of the patients were taken. She was called into work at 2 a.m. to help with the evacuation.
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 damage in Cedar Rapids alone was a preliminary $737 million, Fire Department spokesman Dave Koch said.
The drenching has also severely damaged the corn crop in America's No. 1 corn state and other parts of the Midwest at a time when corn prices are soaring and food shortages have led to violence in some poor countries. But officials said it was too soon to put a price tag on the damage.
At Cedar Rapids' Prairie High School, where 150 evacuees waited, people could be seen crying in the cafeteria, while others watched flood coverage on TVs set up in the gym. Tables were lined with shampoo, toothpaste, contact lens solution and other items, and piles of clothes were separated by size.
At the school, Lisa Armstrong wept as she watched TV news footage of her own rescue. She saw herself climbing into a boat, and watched rescuers trying to coax her dog out of the house. They finally grabbed the animal and pulled it out.
"I didn't think it was going to be as bad as it was, and we should have got out when we were told to leave," she said. "I didn't think or imagine anything like that."
The shelter was the third stop for Don Webster and his family, after his mother-in-law's house and then a stepson's place. Holding his 4-year-old grandson, Leroy, he said he planned to stay for a few days, then "just pray and hope there's something when you go back."
Jeffrey Lucas said that water came pouring into his rental home as he opened the door and dashed out. "I just grabbed what I could and started walking down the road, and I had water up to my chest," Lucas said. He left his cat, Tales, behind.
"I just opened up the cupboards and put the food as high as I could and left one window open just in case," he said. "He was my little buddy."
Cedar Rapids warned people to conserve drinking water after the floodwaters knocked out electricity to all but one of the city's half-dozen or more wells. The one working well was protected by sandbags and generators that were pumping water away from it.
"If we lost that one we would be in serious trouble," Koch said. "We really need to reduce the amount of water we are using, even using paper plates, hand sanitizer."
Hotels implored guests to use water only for drinking.
The city's newspaper, The Gazette, continued to cover the story with the help of emergency generators. But the floodwaters were just outside the front door, and the place had no running water. Portable bathrooms were set up outside for the staff.
"We're putting the paper out through heroic, historic effort by the staff companywide," said Steve Buttry, who started as editor of the newspaper on Tuesday - just one day before the disaster struck.
In Des Moines, fire officials had no immediate estimate of the number of people urged to evacuate several blocks close to the river. Mayor Frank Cownie said the evacuations were an attempt to "err on the side of citizens and residents."
Floodwaters formed a near-moat around Principal Field, the Des Moines ballpark of the minor-league Iowa Cubs, a farm team for the Chicago Cubs.
Interstate 80 was closed east of Iowa City to Davenport after the Cedar River washed over the highway. Amtrak service aboard the California Zephyr was suspended between Omaha, Neb., and Chicago because of flooded-out tracks.