When the Colorado-Big Thompson Project was proposed in 1937, the Western Slope faced a troubling prospect: water from their side of the Continental Divide would be diverted east to thirsty cities along the Front Range. Green Mountain Reservoir was the solution that made the project possible. It compensates Western Slope water users for diversions taken from Lake Granby upstream on the Colorado River. The dam was built between 1938 and 1943 by the Bureau of Reclamation, holding back enough water to honor the complex web of water rights that governs this arid region.

The reservoir does more than store water for agriculture. At its base, the Green Mountain Power Plant generates up to 21,000 kilowatts using two generators. Combined with five other federal power plants in the Colorado-Big Thompson system, it produces enough electricity to power nearly 60,000 homes. But for most visitors, the reservoir's appeal is simpler: clear mountain water stocked with rainbow trout, lake trout, brown trout, and kokanee salmon.

State Highway 9 follows the reservoir's eastern shore, offering travelers views of water and mountains that seem almost too perfect to be real. The small town of Heeney sits on the western bank, and the Green Mountain Reservoir Trail traces the western shoreline for hikers and mountain bikers. At maximum capacity, the lake's surface sits at over 8,000 feet elevation, ringed by peaks of the White River National Forest.