From the Larimer County Parks web site:
Located in the foothills west of Fort Collins at an elevation of 5,430 feet, Horsetooth Reservoir is 1,900 acres of water surrounded by 2,000 acres of public land. It is popular for fishing, boating, water-skiing, and camping. This 6.5-mile reservoir is open year round and is a part of the Colorado-Big Thompson Project operated by the Bureau of Reclamation and the Northern Colorado Water Conservancy District. The purpose of this water project is to divert water from the west slope to the east slope for drinking water, irrigation of farmlands, and generation of hydroelectric power. These agencies control the water level to meet irrigation and power needs.
Recreation is managed by Larimer County Parks and Open Lands. Park Entrance Permits and Camping Fees are required. Park entrance permits ($6-7 per day per vehicle) and boating permits ($6 per day per boat) are required and must be displayed at all times.
In the fall of 2000, the Bureau of Reclamation lowered the water at Horsetooth and began modernizing the four dams. This project is finally finished (Dec 2003) and water levels are returning to normal. As of February 2004, Horsetooth is 80% full.
Homeland security provisions require boats to stay 500 feet away from all Dams. Recreational use on land around the reservoir is still allowed, but only at a distance of 100' away from the dam facilities and structures.