"Some are frail and so it's a very delicate process with them," said Karen Vander Sanden, a hospital spokeswoman.
Water was seeping into the hospital's lower levels, where the emergency generator is located, said Dustin Hinrichs of the Linn County emergency operations center.
"They proactively and preventatively started evacuation basically guessing on the fact they were going to lose power," he said.
Dave Koch, a spokesman for the Cedar Rapids fire department, said the river will crest Friday at about 31.8 feet. It was at 30.9 feet early in the morning. In a 1993 flood, considered the worst flood in recent history, it was at 19.27 feet.
No deaths or serious injuries were reported in Iowa, but one man was killed in southern Minnesota after his car plunged from a washed-out road into floodwaters. Another person was rescued from a nearby vehicle in the town of Albert Lea.
Just southeast of Grand Rapids, Mich., crews pulled the body of a motorist from a car found drifting in the swollen Thornapple River. State police said they believe the 57-year-old man called on his cell phone but didn't say what happened or where he was; they found him using global positioning equipment.
People in several northern Missouri communities, meanwhile, were piling up sandbags to prepare for flooding in the Missouri River, expected to crest over the weekend, and a more significant rise in the Mississippi River expected Wednesday.
Amtrak's California Zephyr line was suspended across Iowa because of flooding along the BNSF Railway. Despite all the water in the town, there was precious little for toilets, cleaning, or drinking.
Koch said the city is at critical levels and only one well was operating. It was in a flood area protected by sandbags, and generators were pumping water away. Normally, the city has six or more functioning wells, he said.
"If we lost that one we would be in serious trouble. Basically we are using more water than we are producing," he said. "We really need to reduce the amount of water we are using ... even using paper plates, hand sanitizer."
Area hotels issued water warnings, including the Marriott Hotel, which issued a statement imploring guests to cut their usage and use water only for drinking.
"Any flushing of the toilet, running the sink, or showering should be kept to a minimum. We understand this is asking a lot, but anyway you may be able to assist us in this time of crisis would go a long way to avoid an even greater disaster."
Gov. Chet Culver declared 83 of the state's 99 counties as state disaster areas. Nine rivers are at or above historic flood levels.
In Des Moines, about 300 volunteers and members of the Iowa Army National Guard worked late Thursday into Friday to shore up a levee showing some soft spots north of downtown. The levee protects a neighborhood along the rising Des Moines River.
They shored up the levee with about 60,000 sandbags, and the levee was holding, said A.J. Mumm, spokesman for the Polk County Emergency Management Agency.
There are about 200 homes in the neighborhood, which is under a voluntary evacuation.