Fern Lake
Addison County, VermontView mapDirections
Nutrients and algae sit mid-range for this region.
↓ down from A at the last regrade
- Mesotrophic
- Impaired · Algal growth
- #5 of 5 in the county
- 42 ft max depth
Fern Lake in Addison County, Vermont has a water quality grade of C (Fair). Water clarity: 20.7 ft visibility. Phosphorus: 19 µg/L. Chlorophyll-a (algae): 5.3 µg/L.
- Clarity
- 20.7 ft
- Max depth
- ~42 ft est.
- Type
- Mesotrophic
- Phosphorus
- 19 µg/L
- Chlorophyll-a
- 5.3 µg/L
- Trend
- ↑ Improving
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Watch Fern Lake’s letter
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Fern Lake is a mesotrophic lake in Addison County, Vermont with an estimated average depth of about 42 feet. Water quality is graded C based on 2 sampling years through 2025. Overall water quality is improving over recent sampling years. Compared to the 4 other monitored lakes in Addison County, Fern Lake ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, VT DEC, last sampled 2025-08-23. Grade methodology: LakeQuality methodology.
What Fern Lake is good for
From access and monitoring records, not editorial picks.
- Clear water20.7 ft of visibility
Swimming Safety
Grade onlyModerate
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 C is nutrients and algae, not a swimming clearance. Fern Lake is listed impaired under Clean Water Act §303(d) (IR 4C) for algal growth, nuisance exotic species. Check local advisories before you swim.
Water Quality Grade: C (Fair)
Crystal clear, you can see 20.7 ft down. Phosphorus 19 µg/L. Chlorophyll-a 5.3 µg/L. TSI 42. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 20.7 ft | Not graded |
| Phosphorus | 19 µg/L | Fair |
| Chlorophyll-a (Algae) | 5.3 µg/L | Fair |
| Trophic State Index (TSI) | 42 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~42 ft est. |
| Average Depth | ~17 ft est. |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Vermont has not published bathymetry for Fern Lake.
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 Fern Lake
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.135 m/yr | 4 |
| Phosphorus | ↓ Declining | +6.06 µg/L/yr | 5 |
| Chlorophyll-a | ↑ Improving | -0.22 µg/L/yr | 5 |
EPA Impairment Status
Fern Lake 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 VT03-04L04_01 · Official waterbody report
County Ranking
Ranked #5 of 5 lakes in Addison County
Nearby Lakes With Higher Grades
Fern Lake holds Grade C. 3 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Addison County
Frequently asked questions about Fern Lake
Where is Fern Lake?
- Fern Lake is a lake in Addison County, Vermont. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Fern Lake?
- Fern Lake in Addison County, Vermont has a water quality grade of C (Fair). Water clarity: 20.7 ft visibility. Phosphorus: 19 µg/L. Chlorophyll-a (algae): 5.3 µg/L.
Is Fern Lake safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Fern Lake is listed impaired under Clean Water Act §303(d) (IR 4C) for algal growth, nuisance exotic species. Check local advisories before you swim.
How deep is Fern Lake?
- No published bathymetric survey covers Fern Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 42 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Explore Fern Lake across LakeQuality
9.7 mi away · 35 ft
Species activity outlook by water temperature and season
Where to stay at Vermont's top lakes, each with its grade
Moderate nutrients, good water quality
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Where this data comes from
149 measurements from 2 monitoring stations, 2021–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Vermont Dept of Environmental Conservation
1VTDECWQ149 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 (2)
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)