"It's to the point now where I think we've done everything we can," said resident Dave Davis, whose neighborhood was filled with backhoes and tractors building an earthen levee. "The only thing now is divine intervention."
Even after the floodwaters crest, the water may not begin receding before Wednesday, creating a lingering risk of a catastrophic failure in levees put together mostly by volunteers.
National Guard troops fanned out in the bitter cold to inspect floodwalls for leaks and weak spots, and residents piled sandbags on top of 12 miles of snow-covered dikes. The freezing weather froze the bags solid, turning them into what townspeople hoped would be a watertight barrier.
Hundreds more Guard troops poured in from around the state and neighboring South Dakota, along with scores of American Red Cross workers from as far away as Modesto, Calif.
The Chicago Red Cross is sending volunteers to help people affected by the flooding. Approximately 12 people were already in the area Friday night or were headed that way. They were expected to open shelters and operate mobile feeding trucks.
One volunteer from Skokie described to ABC7 Chicago what such disasters are like.
"It's very emotional. The first few days aren't too bad, but then people are anxious to get back and see the damage that's done to their homes and get back in as quickly as possible. But that's usually not an option to them because of closed roads and lack of power," Red Cross volunteer Gerald Holmes said.
Homeowners, students and small armies of other volunteers filled sandbags in temperatures that barely rose into the double digits.
The river swelled Friday to 40.67 feet -- more than 22 feet above flood stage and beyond the previous high-water mark of 40.1 feet in 1897. In one flooded neighborhood, a man paddled a canoe through ice floes and swirling currents.
Fargo Mayor Dennis Walaker cautiously expressed hope that the river would stay below 43 feet -- the limit of the reinforced dikes. Walaker said there was not enough time to build the levees any higher.
Fargo escaped devastation from flooding in 1997, when Grand Forks was ravaged by a historic flood 70 miles to the north. This year, the river has been swollen by heavier-than-average winter snows, combined with an early freeze last fall that locked a lot of moisture into the soil. The threat has been made worse by spring rains.
"I think the river is mad that she lost the last time," said engineer Mike Buerkley, managing a smile through his dark stubble as he tossed sandbags onto his pickup truck after working 29 straight hours.
Some 1,700 National Guard troops helped reinforce the dikes and conduct patrols for leaks. Police restricted traffic to allow trucks laden with sandbags, backhoes and other heavy equipment to get through.
Guard member Shawna Cale, 25, worked through the night on a dike, handing up sandbags that were 30 to 40 pounds and frozen-solid.
"It's like throwing a frozen turkey," said sister-in-law Tawny Cale, who came with her husband to help with the sandbags and then to help Shawna move her valuables as she evacuated.
"When it hurts when you lift your arms, you have to stop," Shawna Cale said.
City Administrator Pat Zavoral said the cold firms up the bags, strengthening the dikes. "If you lay loose bags and now they're frozen, they're like a frozen ice cube. It's good shape."
Authorities said they were keeping about 300,000 of the 3 million sandbags they had Friday in warm buildings for use as needed. Sandbags that are already frozen when piled onto a dike do not fit together snugly.
But the freezing temperatures actually helped stave off worse flooding; officials said the river was rising more slowly because the freezing temperatures prevented snow from melting.
The White House said it was monitoring flooding in North Dakota and Minnesota, and President Barack Obama has dispatched the acting head of the Federal Emergency Management Agency to the region. White House spokesman Robert Gibbs said Obama has personally spoken with the governors of both states and with Fargo's mayor.
The president called North Dakota Sen. Kent Conrad on his cell phone during a news conference in Bismarck on flooding problems there and in Fargo. "If there's anything more that we can do, we will do it," Obama said after Conrad held the phone up to a microphone.
Authorities in Fargo and across the river in Moorhead -- a city of about 30,000 people -- expanded evacuations Friday across several blocks. About 2,600 households in Moorhead -- about a third of the city -- were asked to leave their homes. Hundreds more in Fargo were asked to evacuate.
Some residents were roused from their sleep around 2 a.m. Friday and told to leave after authorities found a leak in a dike. They expected to be able to patch it securely.
More than 100 inmates were taken from the county jail in Fargo to other lockups in the region, and Moorhead planned to evacuate the police station because of encroaching floodwaters. U.S. Sen. Byron Dorgan said Northwest Airlines was sending two jetliners to move hospital patients to safer areas.
The effort to fortify flood-prone neighborhoods took place around the city, with officials building a contingency dike system as a second line of defense should the river breach riverside neighborhoods. But some residents were left between the two sets of dikes.
"There are people who are angry about being on the wrong side of the dike," said Tim Mahoney, a Fargo city commissioner whose home is in one of the "wrong-side" neighborhoods.
"We have a 500-year flood that we're combatting, and we think we're doing as well as we can," Mahoney said.
Residents in another of those neighborhoods placed pumps in their yards in hopes of keeping water out of their homes.
Tina Kraft took everything of value or importance in her basement and first floor and moved it upstairs.
"We've prepared for it as best we can," she said. "We really just have to be ready for our house to be flooded."
Deanne Mason and her husband were awakened by the sound of backhoes and tractors building the backup dike.
"I'm not so worried about losing my house," she said. "It's just stuff. But it's emotionally draining to watch this."
In the small town of Oakport Township just north of Moorhead, fire crews watched as a fire destroyed a home surrounded by sandbags that protected it from floodwaters.
Clay County Emergency Operations Center spokesman Dan Olson said fire crews couldn't get closer than 200 feet from the home because the area around it was so flooded. No injuries were reported and the cause of the blaze was not immediately known.
On the Canadian side of the northern-flowing Red River, ice-clogged culverts, ice jams and the rising river threatened Manitoba residents. Several homes were evacuated north of Winnipeg and several dozen houses were flooded.
On the Net: Red River at Fargo water levels: http://sn.im/enwgc
(The Associated Press contributed to this report.)