Horsetooth Reservoir, named for a distinctive local geological outcropping, is the largest reservoir in the Colorado-Big Thompson Project East Slope distribution system. Located west of Fort Collins, the reservoir provides water to Fort Collins, Greeley, smaller domestic suppliers, industries, farms and ranches in the Poudre River Basin.
C-BT Project water is delivered to Horsetooth Reservoir via the Hansen Feeder Canal beginning 13 miles south at Flatiron Reservoir.
Horsetooth Reservoir was built between 1946 and 1949 and began storing water in January 1951. The first water releases were made to the Poudre River in July 1951.
Horsetooth Reservoir has a capacity of 156,735 acre-feet, 1,900 surface acres, 25 miles of shoreline and a maximum depth of 188 feet.