Green Mountain Reservoir
Summit County, Colorado2,125 acresView mapDirections
Colorado WQCD publishes the water-quality measurements for Green Mountain Reservoir. Here is what has been measured.
- Oligotrophic
- 96 ft max depth
- Limited data
Green Mountain Reservoir in Summit County, Colorado has water-quality measurements published by Colorado WQCD, shown here as reported. Water clarity: 11.5 ft visibility. Chlorophyll-a (algae): 1.5 µg/L. Surface area: 2125 acres.
Green Mountain Reservoir is a 2,125-acre cold, clear oligotrophic lake in Summit County, Colorado with an estimated average depth of about 96 feet. Compared to the 2 other monitored lakes in Summit County, Green Mountain Reservoir ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, CDPHE, last sampled 2025-09-11. Methodology: how these readings are compared.
Green Mountain Reservoir covers about 2,100 acres in Summit County. If you are planning to stay, you can search lake houses and cabins around Green Mountain Reservoir on Vrbo, or look for a hotel room near the lake on Booking.com or Expedia.
What Green Mountain Reservoir is good for
From access and monitoring records, not editorial picks.
- Clear water11.5 ft of visibility
- Camping4 public campgrounds nearby
- Big water2,125 acres
Swimming conditions
Readings onlyLimited data
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Green Mountain Reservoir is safe to swim in today is a call for the Water Quality Control Division of the Colorado Department of Public Health and Environment and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Green Mountain Reservoir
These are the measurements Colorado WQCD publishes for Green Mountain Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Good clarity, visible to about 11.5 ft. Chlorophyll-a 1.5 µg/L. TSI 38.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 11.5ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | No reading The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. | |
| Chlorophyll-a (algae) | 1.5µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 38 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Green Mountain Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
~96 ft est.
Surface area
2,125 acres
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Colorado has not published bathymetry for Green Mountain Reservoir.
Lake Size & Watershed
Watershed (drainage) area
576 sq mi
HydroLAKES / HydroSHEDS
Shoreline
15 mi
HydroLAKES / HydroSHEDS
Elevation
7,927 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Recreation & Access
Public campgrounds near Green Mountain Reservoir
- Elliott Creek0.2 km
- Willows2.0 km
- Cow Creek North3.7 km
- Cow Creek South4.1 km
Nearest public campgrounds in the USGS National Map inventory, within about 3 miles. An empty list means USGS records no campground that close, which is not the same as camping being unavailable. Where the source gives an official reservation link, it is used; the cabin and hotel search does not cover campsites. More camping lakes
Stays via Stay22
Stays near Green Mountain Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Green Mountain Reservoir in Summit County, Colorado — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
Top-rated places to stay near Green Mountain Reservoir
Prices for Oct 23–25, 4 adults. Change dates on the map below.
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Fishing Green Mountain Reservoir
Reservoir Info (USACE NID)
Green Mountain Reservoir is a man-made reservoir impounded by the Green Mountain Dam (completed 1943), built primarily for hydroelectric on the Blue River; earth-type dam, 309 ft tall and 1,150 ft long.
- Surface area
- 2,125 ac
- Normal storage
- 153,640 ac-ft
- Max storage
- 161,850 ac-ft
- Drainage area
- 582.48 sq mi
- Hazard class
- High
- Owner
- BUREAU OF RECLAMATION
All listed purposes: Hydroelectric;Irrigation;Recreation.
Source: USACE National Inventory of Dams, NID ID CO01658 · Operator website
Nearby Lakes in Summit County
Frequently asked questions about Green Mountain Reservoir
Where is Green Mountain Reservoir?
- Green Mountain Reservoir is a lake in Summit County, Colorado. Its water-quality measurements are published by Colorado WQCD and shown on this page as reported.
What is the water quality of Green Mountain Reservoir?
- Green Mountain Reservoir in Summit County, Colorado has water-quality measurements published by Colorado WQCD, shown here as reported. Water clarity: 11.5 ft visibility. Chlorophyll-a (algae): 1.5 µg/L. Surface area: 2125 acres.
Is Green Mountain Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
How deep is Green Mountain Reservoir?
- No published bathymetric survey covers Green Mountain Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 96 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 2125 acres.
Are there campgrounds on Green Mountain Reservoir?
- Green Mountain Reservoir has 4 public campgrounds from USGS The National Map within 5 km, including Elliott Creek, Willows, Cow Creek North, Cow Creek South. This is a location join, not a booking. Cabins and hotels are listed separately; campsite reservations use the official link when the source provides one.
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Where this data comes from
6 measurements from 1 monitoring station, 2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Colorado Dept. of Public Health & Environment-WQCD
21COL001_WQX6 samples · 2025
Analytical methods
- Secchi disk depth measurement
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (1)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Lake size & watershed from HydroLAKES (HydroSHEDS)
Public campgrounds from USGS The National Map Structures, within about 3 miles