FARGO, N.D. - As the Red River slowly receded Sunday, Fargo was keeping a close eye on the many kilometres of sandbag levees that are the main line of defense against a potentially destructive flood that has had the city on edge for more than a week.

Residents who spent the better part of the week filling sandbags and building up dikes turned their attention to forming neighbourhood patrols and monitoring levees for breaches. Fargo still fears that water could burst past the levees and submerge parts of the city.

The Army Corps of Engineers and city officials worked overnight to shore up a breach on Fargo's north side, near Oak Grove Lutheran School. The leak, which happened about 1:30 a.m., was contained within hours and wasn't serious enough to warrant the immediate evacuation of nearby residents, said Robyn Litke, a city spokeswoman.

The city had been bracing for a crest of up to 13.10 metres on Sunday, but instead learned Saturday that the river may have reached its peak. The weather service said the river crested around midnight Friday at 12.44 metres. It was at 12.27 metres early Sunday and dropping.

But the river can still fluctuate up to a foot and may remain at dangerous levels for a week, meaning people will have to endure an agonizing several days before they reach the point they can relax.

The city was to resume sandbagging Sunday morning and was requesting more volunteers. Many were expected to turn out after church services that are staple of life on Sunday mornings in Fargo, a heavily Lutheran town of more than 90,000.

"I just hope that everybody doesn't let up. We can't let our guard down," said Al Erickson, a 47-year-old banker whose two-story home is across the street from a golf course that is now a giant water hazard. "The city as a whole will be OK, but there may be neighborhoods that still may have some trouble."

Forecasters say the river is retreating because cold temperatures have been freezing water that normally would be flowing into the river. By the time that water thaws, the biggest flooding threat should have passed, Hudson said.

Officials in charge of the flood-response effort deployed high-tech Predator drone aircraft, called up more National Guard troops and brought in hundreds of bags that each hold a ton of sand and could be dropped by helicopter into breaks in the levees.

The National Guard has been dispatching inspection teams to the levees, joining a cadre of volunteers who are being asked to do the same. The task is monumental, with more than 56 kilometres of levees around Fargo.

"I don't think there's an inch of riverfront on the Fargo side that doesn't have some kind of levee," said city engineer Mark Bittner. "We encourage neighbourhoods to get together and have their own dike patrols and assist us."

Bruce Boelter walked the entire length of a roughly mile-long stretch of sandbag dike to eyeball the manmade wall separating his subdivision and the Red River. Neighbor Tony Guck joined him halfway. Each felt a special stake in the dike they helped build.

"If we don't protect this, it's gonna get us. It's basically for our own security," said Guck, 42. "I'm just planning on coming out every six hours and walking it."

Water has forced hundreds of residents in the Fargo area from their homes and submerged basements and yards in an untold number of houses along the river. Emergency crews in boats had to rescue about 150 people from their homes in neighboring communities in Minnesota, while about 20 per cent of households in Moorhead have been urged to leave.

The flooding was brought on by heavier-than-average winter snows, spring rains and a rapid thaw of the snowpack that sent the Red River to record-high levels in Fargo, North Dakota's largest city.

A winter storm was predicted to hit North Dakota early next week, although the snow isn't expected to affect the flooding in Fargo. Still, wind from the storm could cause 0.6-metre waves that could send some water over the top of dikes, said Dave Kellenbenz, a meteorologist with the National Weather Service.

"That's something we're going to have to watch closely as we move into next week," he said.

The variation in flood forecasts was a roller coaster throughout the week for Fargo, with the projection edging upward twice before being lowered Saturday. Fargo Mayor Dennis Walaker opened a briefing earlier in the day by apologizing for criticizing the weather service.

Greg Gust, a warning coordination meteorologist for the weather service, said the predictions are complex. They come from round-the-clock work by hundreds of scientists, engineers and other experts. Some of those people brave the river for measurements of volume, flow and temperatures. They also use computer models for mathematical and statistical analyses.

But even with improved forecasting methods, the river's record levels and the volatile temperatures don't allow anyone to be certain, and the weather service continued to hedge its prediction Saturday.

The main focus for the Fargo area will be on whether the long line of levees will be able to hold up against the floodwaters -- regardless of their level. Engineers say that anytime water is pressed up against a levee for a considerable period of time, there is a risk of catastrophic flooding.

"The saturation usually becomes the enemy of a levee over time," Jud Kneuvean, chief of emergency management for the U.S. Army Corps of Engineers in Kansas City. "It can cause the embankment to be less stable and slide."

Word of the river's possible retreat couldn't come at a better time for 91-year-old Jim Sundahl, whose Moorhead yard has already been swallowed up by floodwaters. He has been waging a furious battle to keep the waters from his home, where he was born.

"I'm happy about it, I'll tell you that," Sundahl said. "But it won't do us any good for four or five days."