In Lyons, residents took shelter on higher ground, including some at an elementary school, before National Guard convoys could push through the water and into the isolated town. The convoys carried 15 people at a time to buses beyond the roadblocks, past cheering crowds.
One of those onlookers, Holli Stetson, said she was looking for her father, Jerry Boland, who did not evacuate with his wife.
"With no bridges and too much water, there's nowhere to go," Stetson told the Denver Post. "We're just getting more worried by the minute."
To the south, the small community of Jamestown was also out of reach, along with 150 children stuck in summer camps nearby, Boulder County Sheriff's Cmdr. Heidi Prentup said.
The children have plenty of food and water, she said.
The weather service warned Friday of more flash flooding in Loveland. In the town of Drake, the Big Thompson River was more than 4 feet above flood stage. The Big Thompson caused the deadliest flash flood in state history in 1976, when about a foot of rain fell in just four hours, killing 144 people.
Between the Big Thompson and Little Thompson rivers, Jose Ayala spent Friday morning picking through what was left of his family's possessions in their two-story farmhouse near Berthoud.
He and his sons watched the waters rise all Thursday evening, finally making the decision to flee at 11 p.m. with some documents and a computer.
"The rest is in the house. All gone, basically," Ayala said.
President Barack Obama signed an emergency declaration Thursday night, freeing federal aid and allowing the Federal Emergency Management Agency to coordinate disaster-relief efforts.
Some of the flooding was exacerbated by wildfire "burn scars" that have spawned flash floods all summer in the mountains. The flames strip away vegetation that normally helps absorbs excess water and leave a residue behind that sheds water.
One person was killed when a structure in Jamestown collapsed. Another man drowned in floodwaters north of Boulder, and a woman who was with him was missing. She was swept away after the vehicle she was riding in got stuck in water.
The man died after getting out of the vehicle to help her, police said.
To the south, Colorado Springs officers conducting flood patrols found the body of 54-year-old Danny Davis in Fountain Creek on the city's west side.