Green Mountain Reservoir
Summit County, Colorado2,125 acresView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
↑ up from B at the last regrade
- Oligotrophic
- #1 of 3 in the county
- 96 ft max depth
- Limited data
Green Mountain Reservoir in Summit County, Colorado has a water quality grade of A (Excellent). Water clarity: 11.5 ft visibility. Chlorophyll-a (algae): 1.5 µg/L. Surface area: 2125 acres.
- Clarity
- 11.5 ft
- Max depth
- ~96 ft est.
- Area
- 2,125 acres
- Type
- Oligotrophic
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Watch Green Mountain Reservoir’s letter
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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. Water quality is graded A based on 1 sampling years through 2025. 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. Grade methodology: LakeQuality methodology.
What Green Mountain Reservoir is good for
From access and monitoring records, not editorial picks.
- Clear water11.5 ft of visibility
- Camping5 public campgrounds nearby
- Big water2,125 acres
Swimming Safety
Grade onlyLimited data
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The A is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: A (Excellent)
Good clarity, visible to about 11.5 ft. Chlorophyll-a 1.5 µg/L. TSI 38. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 11.5 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | 1.5 µg/L | Good |
| Trophic State Index (TSI) | 38 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~96 ft est. |
| Average Depth | ~69 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
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
- Cataract Creek4.6 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
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
County Ranking
Ranked #1 of 3 lakes in Summit County
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. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Green Mountain Reservoir?
- Green Mountain Reservoir in Summit County, Colorado has a water quality grade of A (Excellent). 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?
- The A is nutrients and algae, 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 5 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.
Explore Green Mountain Reservoir across LakeQuality
Species activity outlook by water temperature and season
Where to stay at Colorado's top lakes, each with its grade
Low nutrients, clear water. The letter is not a swimming clearance.
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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)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated 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