Green Mountain Reservoir lies at the northern end of Summit County, Colorado along the Blue River. The Green Mountain Dam was built between 1938 and 1942 by the United States Bureau of Reclamation. The reservoir and its dam store water to benefit Colorado's Western Slope. Created by President Roosevelt as part of the Colorado-Big Thompson Project in 1937, Green Mountain was the first facility to be constructed. This is because it represents a great compromise that made the C-BT project possible: it compensates the Western Slope for water diverted to cities in Northern Colorado from Lake Granby further upstream on the Colorado River. Water from Green Mountain Dam is released either over the spillway, through the dam, or through the hydroelectric powerplant at the dam's base. The Green Mount