LONGMONT, Colorado (CNN) -- It seems no one is beyond the reach of Colorado's epic flooding.
Fifteen Colorado National Guard members and other emergency workers were stranded Monday on high ground after rising floodwaters the day before forced them to abandon efforts to evacuate residents from flooded areas near Lyons, a National Guard spokeswoman said.
The troops and emergency workers are stuck there until the flooding recedes enough to allow them to drive out, or the weather clears so helicopters can come to rescue them, Colorado Air National Guard Master Sgt. Cheresa Theiral said.
U.S. Army helicopters rescued civilians, as well as some troops and first responders, during a brief lull in the bad weather Sunday that has kept many choppers grounded, according to the National Guard.
However, before the helicopter crews were able to rescue the rest of the troops and emergency workers, the weather turned bad again, the National Guard said.
Unable to ford the high waters despite their specialized vehicles, the 15 rescuers spent the night on high ground, according to the National Guard.
It's a plight shared by as many as 1,000 others stranded by the flooding throughout Colorado's Front Range -- cut off by high waters, isolated even from rescuers driving their specialized high-water trucks, waiting for evacuation by air.
Hundreds of people were assigned to search and rescue efforts in Boulder County alone Monday, the county's Office of Emergency Management said on Twitter.
Rescue crews hoped to resume air rescue efforts Monday, and the forecast will offer some opportunities for aircraft to launch, CNN meteorologist Sherri Pugh said. But spotty rainstorms could keep helicopters grounded periodically, she said.
When the helicopters do get into the air, authorities urged people who are stranded to wave bright cloths, set off flares or signal fires or flash mirrors to get the attention of aircraft passing overhead.
Huge rescue effort
Despite the bad weather, crews from the Colorado and Wyoming National Guards and U.S. Army had used helicopters to rescue more than 700 people as of Saturday night, a National Guard official said.
More than 2,100 people and more than 500 pets had been rescued by air and ground as of late Sunday, according to the National Guard.
The air efforts may be the largest such evacuation in the country since Hurricane Katrina in 2005, National Guard Lt. Col. Mitch Utterback said Saturday.
In some cases, pilots had been flying night missions using night-vision goggles to rescue people, he said.
Among the rescues: Saturday's recovery of 78 children who got stranded while on a field trip.
"The helicopters -- those were the best," said 10-year-old Luca Voeller, one of the students on a field trip to a high-elevation camp when the flooding began.
Death and destruction
Four deaths have been confirmed, with two other people presumed dead.
The four confirmed deaths include a man and a woman, both 19, who were swept away after leaving their car Thursday in Boulder County. Authorities said the woman left the car first, and the man jumped out to try to save her.
Another body was found in a collapsed home in Jamestown in the same county. Rescuers recovered a fourth body on a roadway in Colorado Springs in El Paso County.
Those presumed dead include a 60-year-old woman and an 80-year-old woman, both in Larimer County.
The flooding has washed out or damaged dozens of roads, damaged nearly 18,000 homes and destroyed 1,500.
Boulder County alone will need an estimated $150 million to repair 100 to 150 miles of roadway and 20 to 30 bridges, county transportation director George Gerstle said. The repair bill will be "10 to 15 times our annual budget," he said.
Adding to what is already an unpleasant experience for thousands, residents who have been able to remain in their homes in some towns have been ordered to limit water use and to not flush toilets to avoid sewer backups and other problems. The latest town to issue such an order was Sterling on Monday.
In Firestone, some residents were having to rely on bottled water after two of the city's three water supply lines were destroyed in the flooding, a police department spokeswoman said.
Boulder Mayor Matthew Appelbaum told CNN's "New Day" on Monday that the city will be dealing with the aftermath of flooding for years to come.
"There is a huge amount of damage and a huge amount of repair and a huge amount of cleanup around town that people will be dealing with for a long time," he said.
President Barack Obama signed a major disaster declaration for Colorado on Sunday and ordered federal aid to supplement state and local recovery efforts in Boulder County.
Colorado Gov. John Hickenlooper said he spoke by phone with U.S. Transportation Secretary Anthony Foxx, who "was adamant that the $5 million that was released Friday was just the beginning" of federal assistance.
The situation is "surreal," CNN iReporter Erich Toll said.
"I have never seen anything like it," Toll said Sunday. "There are raging rivers in many places where there have never been rivers -- or even water -- before. There are huge swaths of boulder fields where there used to be parks."
Matthew O'Rourke, an iReporter, said he's fearful of Coal Creek in Lafayette, which threatened to take out his business as it overflowed.
"The currents in the river -- they are impossible to describe how violent and diverse and angry they were and are right now," he said Sunday. "There is no way any human could survive if they were swept into this."
Michael Pearson reported and wrote from Atlanta; George Howell reported from Longmont. CNN's Barbara Starr, Jareen Imam, AnneClaire Stapleton and David Simpson also contributed to this report.
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