In fall 1949, the list of the state’s largest reservoirs by volume looked quite different than it does today. Newly built John Martin Reservoir had gone into operation just months before as the state’s largest reservoir at the time, and Green Mountain Reservoir was showing its value in the Colorado-Big Thompson Project as dedicated storage for the West Slope after being the state’s largest reservoir for five years before that.

In September of that year, however, the list of largest reservoirs would be shuffled again. The gates would close at Granby Dam, creating Lake Granby. At a capacity of 539,758 acre-feet, Lake Granby would hold the title of Colorado’s largest reservoir for more than a decade until the Colorado River Storage Project introduced Blue Mesa Reservoir on the Gunnison River and Navajo Reservoir, which sits mostly in New Mexico but reaches into Colorado.

Lake Granby, the largest reservoir in the Colorado-Big Thompson Project, celebrates 75 years of water storage this month as a key element in the water supply for more than 1 million Colorado residents, and a recreational attraction for people across the country.

Next year, Chimney Hollow Reservoir will join the list of the state’s largest reservoirs, landing at No. 24 on the list.