Seymour Lake
Orleans County, Vermont1,777 acresView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
- Oligotrophic
- #2 of 17 in the county
- 76 ft max depth
- Public access
Seymour Lake in Orleans County, Vermont has a water quality grade of A (Excellent). Water clarity: 24.6 ft visibility. Phosphorus: 7.8 µg/L. Chlorophyll-a (algae): 1.3 µg/L. Surface area: 1777 acres.
- Clarity
- 24.6 ft
- Max depth
- ~76 ft est.
- Area
- 1,777 acres
- Type
- Oligotrophic
- Phosphorus
- 7.8 µg/L
- Chlorophyll-a
- 1.3 µg/L
- Trend
- ↑ Improving
- Public access
- Yes
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Watch Seymour Lake’s letter
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Seymour Lake is a 1,777-acre cold, clear oligotrophic lake in Orleans County, Vermont with an estimated average depth of about 76 feet. Water quality is graded A based on 2 sampling years through 2025. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 16 other monitored lakes in Orleans County, Seymour Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, VT DEC, last sampled 2025-08-15. Grade methodology: LakeQuality methodology.
What Seymour Lake is good for
From access and monitoring records, not editorial picks.
- Clear water24.6 ft of visibility
- Boat launch1 documented ramp
- Big water1,777 acres
Swimming Safety
Grade onlyLow algae
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)
Crystal clear, you can see 24.6 ft down. Phosphorus 7.8 µg/L. Chlorophyll-a 1.3 µg/L. TSI 33. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 24.6 ft | Not graded |
| Phosphorus | 7.8 µg/L | Good |
| Chlorophyll-a (Algae) | 1.3 µg/L | Good |
| Trophic State Index (TSI) | 33 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~76 ft est. |
| Average Depth | ~46 ft est. |
| Surface Area | 1,777 acres |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Vermont has not published bathymetry for Seymour 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.
Recreation & Access
- Seymour LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Seymour Lake
Water Quality Trend: ↑ Improving
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.267 m/yr | 6 |
| Phosphorus | ↑ Improving | -0.49 µg/L/yr | 6 |
| Chlorophyll-a | ↑ Improving | -0.24 µg/L/yr | 6 |
Reservoir Info (USACE NID)
Seymour Lake is a man-made reservoir impounded by the Seymour Lake (completed 1928), built primarily for hydroelectric on the Clyde River-Tr, 12 ft tall and 75 ft long.
- Surface area
- 1,777 ac
- Normal storage
- 0 ac-ft
- Max storage
- 5,200 ac-ft
- Drainage area
- 20.19 sq mi
- Hazard class
- Low
- Owner
- GREAT BAY HYDRO CORP.
Source: USACE National Inventory of Dams, NID ID VT00023 · Operator website
County Ranking
Ranked #2 of 17 lakes in Orleans County
Nearby Lakes in Orleans County
Frequently asked questions about Seymour Lake
Where is Seymour Lake?
- Seymour Lake is a lake in Orleans County, Vermont. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Seymour Lake?
- Seymour Lake in Orleans County, Vermont has a water quality grade of A (Excellent). Water clarity: 24.6 ft visibility. Phosphorus: 7.8 µg/L. Chlorophyll-a (algae): 1.3 µg/L. Surface area: 1777 acres.
Is Seymour Lake safe to swim in?
- The A is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
How deep is Seymour Lake?
- No published bathymetric survey covers Seymour Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 76 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 1777 acres.
Are there boat ramps on Seymour Lake?
- Seymour Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Seymour Lake. Public access is listed as yes.
Explore Seymour Lake 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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Other Grade A Lakes in Vermont
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Where this data comes from
171 measurements from 2 monitoring stations, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Vermont Dept of Environmental Conservation
1VTDECWQ171 samples · 2020–2025
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory