History of the South Platte Collection System

Denver Water's South Platte Collection System includes its largest reservoir, Dillon, as well as dams more than a century old. The system's history is rich with stories of Italian stone masons, a tunnel almost as long as England's Chunnel and pioneers who were ahead of their time in developing ways to deliver water to Denver.

  • Dillon Reservoir

    Crews place concrete in Dillon's outlet works in this 1960 photo. Click image to enlarge (ID# 123.73.15-237). Dillon Reservoir, Denver Water’s largest reservoir, stores water from the Blue River. The water is then diverted into the Roberts Tunnel under the Continental Divide to the North Fork of the South Platte River.

    To build Dillon Reservoir, the entire town of Dillon, 13 miles of highway, eight miles of transmission lines, a hydroelectric generating plant and a forest ranger station had to be relocated. The reservoir nearly doubled Denver’s existing raw water storage facilities, and ranks as one of Colorado’s largest bodies of water.

    Dillon Reservoir was completed in 1963.

  • Harold D. Roberts Tunnel

    This 1954 photo shows the east portal of the Roberts Tunnel, which originally was known as the Blue River Tunnel. Click image to enlarge (ID# 72.22.7965). The Harold D. Roberts Tunnel conveys water stored in Dillon Reservoir under the Continental Divide into the North Fork of the South Platte River.

    The tunnel was under construction for 16 years. The bore is 4,465 feet below the surface, which presented enormous engineering and construction problems.

    At 23.3 miles, it is nearly the same length as the Chunnel under the English Channel.

    The tunnel is named for Harold D. Roberts, attorney and special counsel for the Board, who played a leading role in establishing the right to Blue River water in the mid-1950s.

    The Roberts Tunnel was completed in 1962.

  • Antero Reservoir

    Antero Reservoir is shown in this undated photo. Click image to enlarge. (ID# 44.12.15-5758) Antero Reservoir stores water from the South Platte River watershed and was built to supply the High Line Canal. The name Antero is derived from the Spanish word, “first,” as it was the first dam on the river near the river’s origin and first in storage capacity at the time of construction.

    Geologists believe the reservoir occupies the site of a former lake bed, about 300 years old, called Green Lake.

    Antero Reservoir was completed in 1909.

  • Eleven Mile Canyon Reservoir

    This 1934 photo shows the spillway channel, spillway bridge and top of the dam looking southwest. Click image to enlarge (ID# 263.*.4104). Eleven Mile Canyon Reservoir stores water from the South Platte River watershed. The reservoir is the second largest storage facility in Denver Water’s system and one of the largest bodies of water on Colorado’s East Slope.

    Eleven Mile Canyon Reservoir was completed in 1932.

  • Cheesman Reservoir

    This 1905 photo shows the first time water passed over Cheesman Dam's spillway. Click image to enlarge (ID# 5.67.308). Cheesman Reservoir was the world’s highest dam at the time of construction and was the first reservoir in Denver’s mountain water system. Its completion marked the end of the city’s reliance on streamflow, in-town storage and well supplies.

    Italian stone masons built the dam, which was needed to provide water for the industrial and population growth in Denver.

    The reservoir was named for Walter S. Cheesman, water pioneer and president of the Denver Union Water Company.

    Cheesman Reservoir was completed in 1905.

  • Strontia Springs Reservoir

    This 1982 photo shows crews at the last big concrete pour. Click image to enlarge (ID# 151.26.407).

    Strontia Springs Reservoir is a terminal reservoir that settles and regulates water to Foothills Treatment Plant and to Aurora’s Rampart Reservoir. Waterton Canyon leads to the dam, which also has a hydropower plant that feeds electricity to Denver’s grid.

    Strontia Springs was completed in 1983.

  • Marston Forebay and Conduit 20 Intake Dam

    Marston was the first large-scale storage facility in the Denver area.

    Previously, supply was limited to a few days’ worth of storage at Ashland Reservoir on the west side and Capitol Hill Reservoir in Congress Park, on the east side. Now, a giant conduit transports water to Marston Forebay from the Conduit 20 Intake Dam, three miles upstream of the mouth of Waterton Canyon.

    Marston Forebay was completed in 1902, and Conduit 20 Dam was completed in 1964.

  • Platte Canyon Reservoir and Last Chance Diversion Dam

    Platte Canyon Reservoir is shown in this undated photo. Click image to enlarge (ID# 226.34.114). Platte Canyon Reservoir holds South Platte exchange supplies and once provided storage for the Kassler Filtration Plant, which no longer operates.

    The Last Chance Ditch Diversion Dam diverts South Platte water through a conduit to an underground reservoir at the Kassler Center. From there, water can be pumped to Marston Reservoir or into the nearby Platte Canyon Reservoir.

    Platte Canyon Reservoir was completed in 1904. Last Chance Diversion Dam was completed in 2004 in response to the 2002 drought.