Colorado-Big Thompson Project

The Colorado-Big Thompson Project collects and delivers on average more than 200,000 acre feet of water each year. Most of this water is the result of melting snow in the upper Colorado River basin west of the Continental Divide. The project transports the water to the East Slope via a 13.1-mile tunnel beneath Rocky Mountain National Park. C-BT water flows to more than 640,000 acres of irrigated farm and ranch land and 860,000 people in portions of eight counties within Northern Water boundaries

The C-BT Project consists of:

  • 12 reservoirs
  • 35 miles of tunnels
  • 95 miles of canals
  • Seven hydroelectric power plants
  • 700 miles of transmission lines 
Flatiron ReservoirFlatiron Reservoir Flatiron Reservoir on Colorado’s East Slope is part of the Colorado-Big Thompson Project.

Colorado-Big Thompson Project Map
Water Systems Map
C-BT & Windy Gap Project Statistics

How the C-BT Works

The C-BT Project captures water on Colorado’s West Slope and delivers it beneath the Continental Divide to Northeastern Colorado. Learn more»

C-BT Recreation

See maps, links and other information about boating, camping and other recreational activities on and near the C-BT Project's 12 reservoirs. Learn more»

Power Generation

The C-BT Project generates hydroelectricity as water passes through seven power plants; six on the East Slope and one on the West Slope. Learn more»

Colorado-Big Thompson Interpretive Area

The Interpretive Area at Northern Water’s Berthoud headquarters is a replica of the C-BT Project. Learn more»

West Slope Water Collection

The C-BT Project's West Slope facilities, including Lake Granby and Shadow Mountain Reservoir, collect upper Colorado River basin water and transport it beneath the Continental Divide to the East Slope via the 13.1-mile Alva B. Adams Tunnel. Learn more»

East Slope Water Distribution

On the East Slope C-BT Project water passes through several hydroelectric power plants before the water is stored in Horsetooth Reservoir, Carter Lake and Boulder Reservoir for delivery to farmers, industries and municipalities. Learn more» 

Colorado-Big Thompson Project History

It took nearly two decades to construct the C-BT Project, the largest transmountain water diversion in the state of Colorado. Learn more»