Horsetooth Reservoir (often known locally as Horsetooth) is a large reservoir in southern Larimer County, Colorado just west of the city of Fort Collins, Colorado. The reservoir sits in the foothills above the town on the western side of the Dakota Hogback, which contains the reservoir along its eastern side. The reservoir runs north-south for approximately 6.5 miles (10 km), and is approximately one-half mile (1 km) wide. The reservoir was constructed in 1949 by the Bureau of Reclamation as part of its federal Colorado-Big Thompson Project or "C-BT." Water distribution is currently managed by the Northern Colorado Water Conservancy District and Bureau of Reclamation .