Project History

The Windy Gap Firming Project, of which Chimney Hollow Reservoir is a part of, has been reviewed under the federal National Environmental Policy Act. This review started in 2003. NEPA and Colorado's requirement for a plan focused on fish and wildlife are among several processes in place to identify mitigation measures that will address the project's impacts.

  • 2003


    Project participants enter the federal permitting process and U.S. Bureau of Reclamation holds three formal "scoping" meetings
  • 2005


    U.S. Bureau of Reclamation published two reports, one describing the purpose and need, and one identifying a range of alternatives that could meet the needs
  • 2008


    U.S. Bureau of Reclamation publishes the Draft Environmental Impact Statement
  • 2009


    Municipal Subdistrict offers West Slope benefits to facilitate project implementation
  • 2011


    State officials approve the fish and wildlife mitigation plan and voluntary enhancement plan
  • 2011

    U.S. Bureau of Reclamation publishes the Final Environmental Impact Statement
  • 2012


    Grand County and the Municipal Subdistrict board approve agreements to create improvements to the Colorado River
  • 2014


    U.S. Bureau of Reclamation issues its Record of Decision and signs a carriage contract to transport water to Chimney Hollow Reservoir
  • 2016


    Colorado issues a 401 Water Quality Certification
  • 2017


    U.S. Army Corps of Engineers issues its final Record of Decision
  • 2019

    December 2019

    The Board of Directors of the Northern Water Municipal Subdistrict chooses a contractor to build Chimney Hollow Dam. Barnard Construction Inc. of Bozeman, Mont., will enter into a $485.4 million contract that calls for the construction of a 355-foot-tall asphalt-core dam in the valley west of Carter Lake in southern Larimer County.

The Original Windy Gap Project

The Windy Gap Project was first proposed in 1967 by the cities of Boulder, Estes Park, Fort Collins, Greeley, Longmont and Loveland. Built between 1981 and 1985 and located on the West Slope near Granby, Windy Gap consists of a diversion dam on the Colorado River, a pump plant and a 6-mile pipeline to Lake Granby, the largest storage reservoir in the Colorado-Big Thompson Project system.

The Windy Gap Firming Project will improve the reliability of, or firm, water supplies from the original Windy Gap Project, which started delivering water in 1985. It was understood the original Windy Gap Project would require additional storage to achieve firm water supplies. 

Historic Mitigation

The original Windy Gap Project included years of efforts to determine mitigation measures for direct project impacts, in addition to negotiations for voluntary enhancements. The resulting mitigation measures included funding to benefit endangered fish species as well as water and wastewater treatment facilities.

Voluntary enhancements included a $10.2 million payment to the West Slope in lieu of building Azure Reservoir as well as water supplies for the Middle Park Water Conservancy District.

Additional mitigation included:

  • Endangered species fish mitigation
  • Rancher diversion improvements - upgrades and new pumps
  • Upgrades to Hot Sulphur Springs water and wastewater facilities
  • Salinity studies on the Colorado River
  • Construction of wildlife islands in Windy Gap Reservoir
  • Construction of the Windy Gap Watchable Wildlife Area