"We've lost roads, we've lost bridges, cars, homes," he said. "And we are just now trying to assess the scope of the damage."
Hickenlooper said he will ask President Barack Obama for an emergency declaration, a step toward federal funds to help repair damaged roads, bridges and wastewater plants.
'Not a day to travel'
While at least one shelter was filling up, emergency officials said they had asked few people to evacuate because of the danger of driving through floodwater. The only active evacuation order was in the city of Jamestown, Prentup said.
Pelle urged the rest of Boulder County's 305,000 residents to stay home.
"This is no day to travel," he said. "It's a good day to hunker down and watch the news and find out what's going on."
Many roads in the county were closed or impassable, and city and county offices, schools and even the university were closed Thursday. They will remain closed Friday.
At the university, about 40 buildings sustained mostly minor damage, campus police spokesman Ryan Huff said. School officials had to move 355 graduate students and research faculty members from family housing units because of flooding.
The school also had to relocate 21 undergraduates from two residence halls, he said. The rooms of 11 were so badly damaged, they will have to move for the semester, he said.
No injuries were reported on campus.
Early Thursday, the floodwater in Boulder completely washed out Skunk Creek Trail, a bicycle path that goes underneath 27th Street, according to Drew Landis, who filed images of the creek-turned-raging-rapids to CNN's iReport.
"I'm 6-foot-2 and the creek, which also runs through the underpass, sits about a foot below the height of the footpath," he told CNN. "So that's about 5 to 6 feet of rushing water."
An area where homeless people often camp just south of the campus near Skunk Creek was under 5 feet of water Thursday, graduate student Alan Smith said.
He described water pouring down bike paths and out of drainpipes.
"It's really cool to see these conduits spewing out water from the base of these buildings," Smith said. "It's like a Super Soaker. They're spewing water several feet away."