A sandbagged levee was holding in Cedar Falls on Wednesday, protecting the downtown from the raging Cedar River.
But just downriver, the neighboring city of Waterloo ordered a mandatory evacuation of some neighborhoods because of groundwater runoff, officials said.
Waterloo Mayor Tim Hurley said as many as 60 homes will be affected by the evacuation with about half that many businesses and some city offices.
"This is not a recommendation, this is not an encouragement, this is a mandatory evacuation. We need you out of there," Hurley said during a morning news conference.
The problem was caused by the backup of stormwater in the city of 65,000, he said.
Hurley also said volunteers were being pulled out of the area.
"Certainly, we don't want volunteers down there and stranded," Hurley said.
National Guard soldiers had blocked off bridges in and out of the downtown.
Patrice Calhoun, of Waterloo, rolled up her pants and took off her shoes to wade through water to get home Wednesday morning.
"Everything is flooded - everything is up to knee-high," she said. "You could actually swim in it."
Clifton Sallis, owner of Brothaz Barbershop in Waterloo, said everyone on his block helped sandbag, but he's still worried.
"I hope it don't flood over," he said. "If it rains, one rain will do it."
In Cedar Falls, a city of about 35,000 people, officials were relieved that a frantic sandbagging effort had kept flood waters out of downtown.
City spokeswoman Susan Staudt said thousands of volunteers showed up Tuesday to help with sandbagging along the levee protecting downtown.
"Our volunteers saved this city, but we are still at a critical point," she said.
* Locally: The Little Sioux River at Linn Grove was nearing 18.5 feet late Wednesday, nearly half a foot above flood stage, and still slowly rising.