Green River Reservoir
Lamoille County, Vermont625 acresView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
- Oligotrophic
- Impaired · Hydrologic alteration
- #5 of 6 in the county
- 63 ft max depth
- Limited data
Green River Reservoir in Lamoille County, Vermont has a water quality grade of A (Excellent). Water clarity: 13.1 ft visibility. Phosphorus: 7.4 µg/L. Chlorophyll-a (algae): 1.4 µg/L. Surface area: 625 acres.
- Clarity
- 13.1 ft
- Max depth
- ~63 ft est.
- Area
- 625 acres
- Type
- Oligotrophic
- Phosphorus
- 7.4 µg/L
- Chlorophyll-a
- 1.4 µg/L
- Trend
- ↓ Declining
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Watch Green River Reservoir’s letter
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Green River Reservoir is a 625-acre cold, clear oligotrophic lake in Lamoille County, Vermont with an estimated average depth of about 63 feet. Water quality is graded A based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. Compared to the 5 other monitored lakes in Lamoille County, Green River Reservoir ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, VT DEC, last sampled 2025-08-18. Grade methodology: LakeQuality methodology.
What Green River Reservoir is good for
From access and monitoring records, not editorial picks.
- Clear water13.1 ft of visibility
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. Green River Reservoir is listed impaired under Clean Water Act §303(d) (IR 4C) for hydrologic alteration. Check local advisories before you swim.
Water Quality Grade: A (Excellent)
Good clarity, visible to about 13.1 ft. Phosphorus 7.4 µg/L. Chlorophyll-a 1.4 µg/L. TSI 36. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 13.1 ft | Not graded |
| Phosphorus | 7.4 µg/L | Good |
| Chlorophyll-a (Algae) | 1.4 µg/L | Good |
| Trophic State Index (TSI) | 36 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~63 ft est. |
| Average Depth | ~33 ft est. |
| Surface Area | 625 acres |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Vermont has not published bathymetry for Green River 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.
Fishing Green River Reservoir
Water Quality Trend: ↓ Declining
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.75 m/yr | 3 |
Reservoir Info (USACE NID)
Green River Reservoir is a man-made reservoir impounded by the Green River Dam (completed 1947), built primarily for hydroelectric on the Green River; arch-type dam, 105 ft tall and 360 ft long.
- Surface area
- 625 ac
- Normal storage
- 16,900 ac-ft
- Max storage
- 16,900 ac-ft
- Drainage area
- 14.6 sq mi
- Hazard class
- High
- Owner
- Village of Morrisville, VT
All listed purposes: Hydroelectric;Recreation.
Source: USACE National Inventory of Dams, NID ID VT00024 · Operator website
EPA Impairment Status
Green River Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 4C).
Causes of impairment
Source: EPA ATTAINS assessment unit VT07-18L03 · Official waterbody report
County Ranking
Ranked #5 of 6 lakes in Lamoille County
Nearby Lakes in Lamoille County
Frequently asked questions about Green River Reservoir
Where is Green River Reservoir?
- Green River Reservoir is a lake in Lamoille County, Vermont. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Green River Reservoir?
- Green River Reservoir in Lamoille County, Vermont has a water quality grade of A (Excellent). Water clarity: 13.1 ft visibility. Phosphorus: 7.4 µg/L. Chlorophyll-a (algae): 1.4 µg/L. Surface area: 625 acres.
Is Green River Reservoir safe to swim in?
- The A is nutrients and algae, not a swimming clearance. Green River Reservoir is listed impaired under Clean Water Act §303(d) (IR 4C) for hydrologic alteration. Check local advisories before you swim.
How deep is Green River Reservoir?
- No published bathymetric survey covers Green River Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 63 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 625 acres.
Explore Green River Reservoir across LakeQuality
Species activity outlook by water temperature and season
Where to stay at Vermont'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
48 measurements from 1 monitoring station, 2021–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Vermont Dept of Environmental Conservation
1VTDECWQ48 samples · 2021–2025
Analytical methods
- EPA approved Alternate Test Procedure for 4500 P H. Has a 28 day hold without acid preservation.
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- 2130 B ~ Nephelometric Method
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
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)