Grand Lake

Grand Lake is the largest natural water body in Colorado. The lake’s beauty and proximity to the west entrance of Rocky Mountain National Park draws thousands of visitors annually. Boating and fishing on Grand Lake and hiking in the nearby Arapaho National Forest are popular activities. See the C-BT Recreation - West Slope page for more information.

Last West Slope Stop for C-BT Project WaterGrand Lake plays a key role in the Colorado-Big Thompson Project as the last West Slope stop for C-BT water headed to the East Slope. Water enters the Alva B. Adams Tunnel's West Portal on Grand Lake's eastern shore before traveling 13 miles to the tunnel's East Portal above Estes Park. The West Portal is near the East Inlet trailhead into Rocky Mountain National Park.

Grand Lake
Grand Lake

Water Fluctuation Minimized C-BT Project operations minimize fluctuations in Grand Lake’s level to one vertical foot or less. Grand Lake has a capacity of 68,600 acre-feet of water, 4.5 miles of shoreline, 515 surface acres and a maximum depth of 265 feet.

In the 1880s, the Colorado State Legislature funded two studies to evaluate the feasibility of bringing irrigation water from the Grand Lake area to Colorado’s East Slope. By the late 1930s this idea had culminated in the C-BT Project, which was constructed from 1938 to 1957.