Gross Reservoir, located in Boulder County, Colorado, is owned and operated by Denver Water.

Completed in 1954, the reservoir has a surface area of 440 acres (180 ha), and the spillway sits at 7,225 feet (2,202 m) elevation.

The reservoir receives water from South Boulder Creek and the western side of the Continental Divide through the Moffat Tunnel.

[3] Construction on the project, expected to be complete around 2027,[4] will raise the level of the dam by 131 feet (40 meters), resulting in an additional 77,000 acre-feet (95,000,000 cubic meters) of water storage capacity in the reservoir and making it the tallest dam in Colorado.

Boulder County announced in spring 2019 that it would require Denver Water to obtain a land use permit under Colorado law before commencing the expansion project.