Moving Water in the Watershed

Most of the water that falls or flows in the Blue River watershed ends up passing through the area’s reservoirs and tunnels—collectively known as transmountain diversion facilities—before reaching its final destination. A transmountain diversion in the Blue River watershed represents the removal and transport of water across the Continental Divide.

Lake Dillon in ColoradoColorado water law provides for transmountain diversions by allowing the movement of water from its source to where it is needed within the state, regardless of distance. These diversions are 100% consumptive, meaning no water from the diversion will return to the basin of origin’s waters as return flow.

Several diversion facilities exist in the watershed and are described here. According to the Colorado River Water Conservation District, there is no current or reasonably foreseeable need for new diversion projects.

Transmountain diversion of Colorado River water results in adverse economic, environmental, and recreational impacts. Front Range water demands can be met through a combination of better groundwater management, conservation, reuse, system interconnections, re-operations, and in-basin transfers and exchanges. For more about transmountain water diversions, see


Two reservoirs exist within the Blue River watershed, Dillon Reservoir in the heart of Summit County and Green Mountain Reservoir in north Summit County, 13 miles southeast of the town of Kremmling.

Dillon Reservoir

Sunset over Lake DillonDillon Reservoir is one of Denver Water’s main storage facilities, locally known as Lake Dillon. The reservoir dams the upper portion of the Blue River and releases to the lower Blue River.

Dillon Reservoir is only one part of a large and complex water system. There are many components that affect reservoir levels, including releases from other reservoirs, precipitation and drought conditions.

  • Developed, owned and operated by Denver Water;
  • Stores up to 254,000 a/f of water;
  • Diverts water through the Roberts Tunnel.

Green Mountain Reservoir

Green Mountain Reservoir was completed in 1943 by the United States Bureau of Reclamation as part of the Colorado Big Thompson Project.

The reservoir dams the lower portion of the Blue River and provides for west slope water storage with a compensatory storage provision that allows for present and future uses on the east slope.

  • Owned and operated by the Bureau of Reclamation;
  • Dual powerplant generates 21,600 kilowatts of electric power;
  • Stores up to 153,639 a/f of water;
  • Releases and stores water on a priority system to and for various interests under the rules of the CBT.


Five tunnels divert water from the Blue River and its two reservoirs to East Slope (Front Range) communities. These are what define transmountain diversions here—the movement water from west of the Continental Divide (Divide) to east of the Divide.

Most of Colorado’s mountain communities and recreational environments are considered to be west of the Divide, where most of the state’s surface water collects. On the other hand, the majority of growth occurs in the large metropolitan areas east of the Divide. Therefore, in order to provide water for the population centers, water must be diverted and delivered through tunnels from west to east.

Roberts Tunnel (Summit County to Park County)

  • Owned by the Denver Water Board;
  • Longest major water delivery tunnel in the world (23.3 miles);
  • Diverts water from the bottom of Dillon Reservoir and under the Continental Divide;
  • Discharges near the town of Grand in Park County;
  • Diverts approximately 63,000 acre feet (a/f) of water per year.

Hoosier Pass Tunnel (Summit County to Park County)

  • Owned by the city of Colorado Springs;
  • Diverts water out of the upper Blue River and its tributaries above Fairplay, where it is stored in Montgomery Reservoir;
  • Travels through the tunnel where it discharges into the South Platte and Middle Fork Rivers;
  • Diverts approximately 9,600 a/f of water per year.

Vidler Tunnel (Summit County to Clear Creek County)

  • Owned by the City of Golden;
  • Water used primarily for augmentation and municipal purposes in the Clear Creek Basin. Water can also be used for augmentation water in the Blue River Watershed.
  • Diverts water from Peru Creek, a Blue River tributary, under Argentine Pass;
  • Discharges into Leavenworth Creek, a tributary of Clear Creek;
  • Diverts approximately 740 a/f of water per year.

Straight Creek Tunnel (Summit County to Clear Creek County)

  • Owned by the Colorado Department of Transportation and Coors Brewing Company, which shares the water with its lessees;
  • Diverts water from Straight Creek to a tunnel under the Continental Divide just west of Eisenhower Tunnel;
  • Discharges into Clear Creek;
  • Diverts approximately 460 a/f of water per year.

Boreas Pass Ditch (Summit County to Park County)

  • Owned by the City of Englewood for municipal purposes;
  • Diverts water from Indiana Creek, a tributary of the upper Blue River;
  • Discharges into North Tarryall Creek, a tributary of the South Platte River;