The river otter is a Colorado state threatened species that looks to be making a comeback in Boulder County, including in St. Vrain Creek.
A sleek brown body surged through the water. A broad head turned, and curious eyes surveyed the astounded onlookers. A muskrat? A mink? No, a river-otter! After an absence of almost half a century, they are coming back.
Source: February Nature Almanac: River otters resurge in Boulder County – Boulder Daily Camera
