• Length: 25 Miles
• Surface Area: 2,040 Acres
• Volume: 156,735 Acre Feet
• Drainage Area: 17 Square Miles
• Average Depth: 82 Feet
• Maximum Depth: 200 feet
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, and is approximately one-half mile 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 . Horsetooth and Carter Lake serve as the two principal containers for water diverted eastward under the continental divide via the C-BT.
The reservoir is a supplementary source of municipal water for Fort Collins and other communities in the region, as well as for irrigation in the South Platte River valley. The reservoir takes its name from Horsetooth Mountain, a summit in the foothills west of the southern end of the reservoir.
The construction of the reservoir inundated the community of Stout. Prior to construction, the majority of the town moved to a location that today surrounds Horsetooth's South Bay, but a few building foundations, including that of the old school house, are now under water. The reservoir has a capacity of 156,735 acre feet, a total shoreline of 25 miles. The reservoir is located roughly at 40.55436°N 105.15591°W. In recent history the reservoir has experienced relatively low water levels, but in 2014 experienced record highs. It reached 98.6% of its capacity in June 2014, the highest it has been in four years.
The reservoir is a popular recreation destination for the region. According to a recent study conducted by Reclamation and the recreation manager at Horsetooth, Larimer County Parks and Open Lands, approximately 570,000 visitors come to Horsetooth every year. Surrounded by 1,900 acres of public lands. Larimer County has provided recreation management at Horsetooth, and three other C-BT reservoirs, since they opened in the early 1950s.
Recreational boating is popular during summer months and swimming is allowed at the specifically designated Swim Beach maintained by LCPOL as well as in some of the coves. Kayaking and canoeing is also popular. Fishing is also highly popular from boats or from shore, but is no longer allowed from the dams due to security concerns. Since the late 1960s, the sport of bouldering has become an established climbing pastime at the reservoir, the hard Dakota sandstone providing many challenging problems for both American and foreign athletes. However cliff diving is not allowed near the reservoir due to safety concerns. . Cliff diving/jumping in the water is extremely dangerous and prohibited in all areas of Horsetooth. Park rangers patrol the reservoir for violators to keep everyone enjoying the reservoirs safety. Road cycling around Horsetooth has also become popular as has hiking and mountain biking, particularly along the Foothills Trail that traverses the reservoir's eastern edge. The City of Fort Collins maintains several open spaces directly below the reservoir and the State-owned Lory State Park is along the reservoir's northwestern shore.
Other ridge lines surrounding the reservoir have become the site of residential development in recent decades, with structures ranging from get-away-cabins to luxury homes.