A red sun low over Slim Lake through wildfire haze, its reflection a column of orange on the water

Reservoirs in Colorado

74 of 733 measured Colorado lakes (10%) are man-made reservoirs in the USACE National Inventory of Dams. 69 carry a High or Significant hazard rating.

Reading the Colorado reservoir landscape

74 reservoirs in Colorado appear in the USACE National Inventory of Dams. That's a meaningful share — reservoir lakes carry their own ecology and access patterns distinct from natural lakes, including managed water levels, drawdowns timed to the dam's purpose, and shoreline mix dominated by structures built post-impoundment.

Colorado's reservoirs serve a mix of purposes — flood control, water supply, hydroelectric power generation, navigation, and recreation often co-exist on the same impoundment, with one designated as the primary and others as secondary. The operating rules (pool levels, release schedules, drawdown timing) follow the primary purpose, which shapes everything from shoreline access through fish-population dynamics through year-round recreational use patterns.

The USACE National Inventory of Dams (NID) catalogs every dam in the United States above a size threshold — typically 25 feet in height or 50 acre-feet in maximum storage, plus all dams classified as high-hazard regardless of size. The reservoir records below pull NID fields (year built, hazard class, maximum storage, surface area at normal pool, dam length, primary purpose) and pair them with water-quality data where the impoundment also appears in EPA's lake-monitoring inventory.

Why these Colorado reservoirs were built

Irrigation

Recreation

Flood Risk Reduction

Fish and Wildlife Pond

Hydroelectric

Water Supply

Total reservoirs

100,614

Total surface acres

3,607,854

Normal storage (ac-ft)

High or Significant hazard

All 74 Colorado reservoirs (by surface area)

Reservoir	County	Surface area	Year built	Purpose	Hazard
John Martin Reservoir	Bent	11,590 ac	1943	Flood Risk Reduction	High
Lake Granby Dam Bottom	Grand	7,260 ac	1950	Hydroelectric	High
Lake Meredith	Crowley	6,223 ac	1926	Irrigation	Significant
Pueblo Reservoir	Pueblo	5,671 ac	1975	Flood Risk Reduction	High
Adobe Creek Reservoir	Bent	5,094 ac	1904	Irrigation	High
Mcphee Reservoir	Montezuma	4,918 ac	1983	Fish and Wildlife Pond	High
Nee Noshe Reservoir	Kiowa	3,696 ac	1896	Irrigation	Significant
Carter Reservoir	Larimer	3,551 ac	1952	Hydroelectric	High
Antero Reservoir	Park	3,446 ac	1909	Water Supply	High
Dillon Reservoir	Summit	3,300 ac	1963	Water Supply	High
North Sterling Reservoir	Logan	2,880 ac	1948	Irrigation	High
Milton Reservoir	Weld	2,660 ac	1911	Irrigation	High
Jackson Reservoir	Morgan	2,427 ac	1900	Irrigation	High
Prewitt Reservoir	Washington	2,329 ac	1912	Irrigation	High
Green Mountain Reservoir	Summit	2,125 ac	1943	Hydroelectric	High
Shadow Mountain Lake	Grand	1,852 ac	1946	Irrigation	High
Barr Lake	Adams	1,830 ac	1893	Irrigation	High
Turquoise Reservoir	Lake	1,788 ac	1968	Irrigation	High
Boyd Lake	Larimer	1,747 ac	1900	Fish and Wildlife Pond	High
Wolford Mountain Reservoir	Grand	1,550 ac	1995	Irrigation	High
Lake Nighthorse	La Plata	1,548 ac	2008	Water Supply	High
Trinidad Reservoir	Las Animas	1,442 ac	1976	Flood Risk Reduction	High
Standley Lake	Jefferson	1,222 ac	1913	Irrigation	High
Lake Henry	Crowley	1,194 ac	1914	Irrigation	High
Chatfield Reservoir	Jefferson	1,150 ac	1973	Flood Risk Reduction	High
Vega Reservoir	Mesa	1,109 ac	1959	Irrigation	High
Ridgway Reservoir	Ouray	1,109 ac	1987	Flood Risk Reduction	High
Steamboat Lake	Routt	1,056 ac	1966	Recreation	High
Platoro Reservoir	Conejos	1,000 ac	1951	Flood Risk Reduction	High
Cherry Creek Reservoir Top	Arapahoe	852 ac	1953	Flood Risk Reduction	High
Cherry Creek Reservoir Bottom	Arapahoe	852 ac	1953	Flood Risk Reduction	High
Stagecoach Lake	Routt	819 ac	1988	Water Supply	High
Elkhead Reservoir	Moffat	724 ac	1979	Fish and Wildlife Pond	High
Union Reservoir	Weld	717 ac	1902	Irrigation	Significant
Horse Creek Outlet Lake	Weld	712 ac	1910	Irrigation	High
Kenney Reservoir	Rio Blanco	615 ac	1984	Hydroelectric	High
Lake John	Jackson	612 ac	1957	Recreation	Significant
Mountain Home Reservoir	Costilla	597 ac	1908	Irrigation	High
Douglas Reservoir	Larimer	565 ac	1901	Irrigation	High
Rifle Gap Reservoir	Garfield	435 ac	1967	Irrigation	High
Clear Creek Reservoir	Chaffee	425 ac	1910	Water Supply	High
Miramonte Reservoir	San Miguel	410 ac	1978	Recreation	High
Crawford Reservoir	Delta	406 ac	1962	Irrigation	High
Prospect Lake	Weld	398 ac	1914	Irrigation	Significant
Harvey Gap Reservoir	Garfield	320 ac	1892	Irrigation	High
Willow Creek Reservoir	Grand	303 ac	1953	Irrigation	High
Crystal Reservoir	Montrose	301 ac	1977	Hydroelectric	High
Rampart Reservoir	El Paso	300 ac	1970	Hydroelectric	High
Deweese Reservoir	Custer	295 ac	1903	Irrigation	High
Chambers Lake	Larimer	281 ac	1924	Irrigation	High
North Delaney Lake	Jackson	258 ac	1971	Irrigation	Low
Lon Hagler Reservoir	Larimer	201 ac	1967	Irrigation	High
Windsor Lake	Weld	197 ac	1904	Irrigation	High
Martin Lake	Huerfano	190 ac	1910	Recreation	High
Horseshoe Reservoir	Huerfano	172 ac	1961	Recreation	High
Pearl Lake	Routt	166 ac	1962	Recreation	High
Island Lake	Delta	161 ac	1954	Irrigation	Significant
Eggleston Lake	Delta	158 ac	1949	Irrigation	High
Highline Lake	Mesa	155 ac	1967	Recreation	High
Rio Blanco Lake	Rio Blanco	149 ac	1970	Recreation	Low
Sweitzer Reservoir	Delta	139 ac	1954	Recreation	High
Beaver Creek Reservoir	Rio Grande	130 ac	1912	Recreation	High
Big Meadows Reservoir	Mineral	115 ac	1968	Recreation	High
Windy Gap Reservoir	Grand	108 ac	1985	Irrigation	Significant
Jumbo Annex Lake	Logan	100 ac	1977	Fish and Wildlife Pond	Low
Skaguay Reservoir	Teller	88 ac	1901	Recreation	Significant
Dowdy Lake	Larimer	83 ac	1962	Recreation	Significant
Dome Lake Lower	Saguache	75 ac	1975	Fish and Wildlife Pond	Low
Big Creek Reservoir	Mesa	63 ac	1893	Irrigation	High
Haviland Lake	La Plata	61 ac	1927	Fish and Wildlife Pond	High
Prospect Lake	El Paso	51 ac	1954	Recreation	Significant
Lake Isabel	Custer	35 ac	1937	Recreation	High
Turks Pond	Baca	33 ac	1952	Recreation	Low
Stalker Lake	Yuma	20 ac	1956	Fish and Wildlife Pond	Significant

Frequently Asked Questions

How many reservoirs are in Colorado?

74 of 733 measured Colorado lakes (10%) are man-made reservoirs in the USACE National Inventory of Dams. 69 are rated High or Significant hazard, meaning failure would put downstream lives or property at substantial risk. The oldest matched dam dates to 1892.

What's the largest reservoir in Colorado?

The largest matched reservoir in Colorado is John Martin Reservoir in Bent County at 11,590 acres of normal surface area, impounded by the John Martin Dam (completed 1943).

What's the difference between a reservoir and a natural lake?

A reservoir is a body of water impounded by a man-made dam — typically built for flood control, hydroelectric power, water supply, irrigation, or recreation. A natural lake formed without human intervention, usually from glacial scouring, volcanic activity, or river meandering. Reservoirs typically have shoreline that fluctuates with seasonal water level management, while natural lakes have more stable shorelines. The USACE National Inventory of Dams classifies every regulated dam in the United States, which is how we identify which LakeQuality lakes are actually reservoirs.

What does the hazard class mean?

USACE assigns each dam a hazard potential classification based on what would happen downstream if the dam failed — NOT how likely the dam is to fail. "Low" hazard means dam failure would cause no probable loss of life and only low economic loss. "Significant" means probable loss of life is unlikely but appreciable economic damage would occur. "High" means probable loss of life and significant economic damage. The classification is about consequence, not condition. Many High-hazard dams are perfectly safe; they're rated High because populated areas have grown downstream over time.

Where does this reservoir data come from?

Every reservoir record on this page is matched to the USACE National Inventory of Dams (NID), the federal database of all dams ≥25 ft tall or impounding ≥50 acre-feet, plus any dam that poses a Significant or High hazard regardless of size. The NID is published by the U.S. Army Corps of Engineers and updated annually. Surface area, storage capacity, dam height, and hazard classification come directly from NID records.

Where to stay near Colorado reservoirs

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More on reservoirs and water quality

Are Reservoirs Cleaner Than Natural Lakes?

Dam-built reservoirs and natural lakes compared side by side on the same nutrient and algae measurements — the gap, the reasons behind it, and the exceptions.

Do Deeper Lakes Have Better Water Quality?

Surveyed maximum depth against nutrient and algae readings: the pattern, the shallow lakes that still read clean, and why land use beats bathymetry.

Lake Water Quality Explained: What the Readings Mean

How nutrient and algae readings are read against EPA ecoregion condition classes, what each class means in the water, and why a clean reading is not a clearance.

Why Lakes Turn Green: Phosphorus and Nutrient Pollution

How phosphorus and nutrient runoff drive algae growth and turn lakes green, where the nutrients come from, and what it means for a lake’s readings.

Data source

Reservoir data from the USACE National Inventory of Dams (NID), the federal database of all regulated dams. Dam attributes (height, year completed, storage capacity, hazard class) are matched to LakeQuality lakes by proximity and dam-name similarity. Some lakes may be reservoirs that aren't matched if the dam record uses a name substantially different from our lake name.