The pictures of the otter, taken as the animal was eating a fish along Boulder Creek east of the city's downtown, provide hope the species could make a comeback in the Boulder area, wildlife experts said.
"It actually sat in front of the camera for several more minutes, sitting there munching on the fishtail," Christian Nunes, a wildlife ecology technician for Boulder Open Space, said in an interview with The Daily Camera newspaper.
Boulder Open Space placed the motion-activated camera along Boulder Creek.
"I was extremely surprised," Nunes said. "It's a species that is quite rare in Colorado."
North American river otters are found in Canada and much of American West and Southeast, but spreading development has driven them away from many metropolitan areas such as Boulder.
The species is still considered endangered by the Colorado Parks and Wildlife Department.
"We don't really have population estimates [for otters] anywhere in the state," the department's Eric Odell said.