With Boulder Creek is at its highest level since the county began seeing widespread flooding, officials have ordered evacuations for the city at the mouth of Boulder Canyon.
The evacuation order is for all residents along Boulder Creek from the mouth of Boulder Canyon east to Broadway between Marine and Pearl streets.
City officials said that includes about 4,000 residents.
Around 2 a.m., officials said they did not have a timetable for lifting the evacuation order. Boulder Creek at that point was moving at 3,400 cubic feet per second, down from nearly 5,000 cubic feet per second at the time the evacuations were ordered.
All residents are warned to go to higher ground immediately due to the potential for flash flooding along the creek.
Boulder emergency officials, however, say evacuees should leave on foot and not drive as many city streets are impassable.
Residents north of Boulder Creek should move at least to Spruce Street, if not further. Residents south of Boulder Creek should move past Euclid Street.
Another 4,000 residents near Boulder Creek east of Broadway to 75th Street are urged to "shelter in place" on high ground.
Flood sirens have been activated throughout downtown Boulder.
Officials say there are mudslides at the mouth of Boulder Canyon 400 feet long and 4 feet deep as the sides of the canyon give way due to the saturation from the days long rain.
Boulder County emergency officials are worried that the mud and rock slides will clog Boulder Creek, causing water to collect upstream and then release, causing a sudden surge in water volume downstream.