Sunapee Lake
Sunapee Lake in Sullivan County, New Hampshire has a water quality grade of A (Excellent). Phosphorus: 5 µg/L. Chlorophyll-a (algae): 1.1 µg/L. Surface area: 4090 acres.
- Area
- 4,090 acres
- Type
- Oligotrophic
- Public access
- Yes
Sunapee Lake is a 4,090-acre cold, clear oligotrophic lake in Sullivan County, New Hampshire. Water quality is graded A based on 2 sampling years through 2024. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 23 other monitored lakes in Sullivan County, Sunapee Lake ranks #12 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2024-09-16. Grade methodology: LakeGrade methodology.
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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.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
No clarity data. Phosphorus level: 5 µg/L. Chlorophyll-a: 1.1 µg/L. Trophic State Index: 29.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 5 µg/L | Good |
| Chlorophyll-a (Algae) | 1.1 µg/L | Good |
| Trophic State Index (TSI) | 29 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Sunapee Lake
Compare lakeside cabins, hotels, and vacation rentals near Sunapee Lake in Sullivan County, New Hampshire — 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 Sunapee Lake
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Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 4,090 acres |
| Public Access | Yes |
No bathymetric survey has been published for Sunapee Lake, so its depth is not documented here.
Recreation & Access
- Sunapee HarborPublic
Named access points from the USGS National Boat Ramps inventory, snapped within 5 km. More lakes with boat ramps
Fishing Sunapee Lake
Reservoir Info (USACE NID)
Sunapee Lake is a man-made reservoir impounded by the Sunapee Lake Dam (completed 1872), built primarily for recreation on the Sugar River; concrete-type dam, 14 ft tall and 80 ft long.
- Surface area
- 4,090 ac
- Normal storage
- 19,800 ac-ft
- Max storage
- 40,900 ac-ft
- Drainage area
- 44.8 sq mi
- Hazard class
- Significant
- Owner
- NH DES WATER DIVISION
Source: USACE National Inventory of Dams, NID ID NH00108 · Operator website
EPA Impairment Status
Sunapee Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit NHLAK801060402-05-01 · Official waterbody report
County Ranking
Ranked #12 of 24 lakes in Sullivan County
Nearby Lakes in Sullivan County
Frequently asked questions about Sunapee Lake
Where is Sunapee Lake?
- Sunapee Lake is a lake in Sullivan County, New Hampshire. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Sunapee Lake?
- Sunapee Lake in Sullivan County, New Hampshire has a water quality grade of A (Excellent). Phosphorus: 5 µg/L. Chlorophyll-a (algae): 1.1 µg/L. Surface area: 4090 acres.
Is Sunapee Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Sunapee Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 1.1 µg/L. Always check local health department advisories before swimming.
Are there boat ramps on Sunapee Lake?
- Sunapee Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Sunapee Harbor. Public access is listed as yes.
Explore Sunapee Lake across LakeGrade
More New Hampshire Lake Rankings
Top 25 by overall water quality score
Top 25 by Secchi water clarity
Grade A/B + low algae filter
Panfish-rich, public access
Full state directory
Other Grade A Lakes in New Hampshire
Oligotrophic Lakes in New Hampshire
Where this data comes from
76 measurements from 6 monitoring stations, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- New Hampshire Department Of Environmental Services (BEACH)
1111330076 samples · 2020–2024
Analytical methods
- Phosphorus by Two Reagent Colorimetry
- CHLOROPHYLL A-B-C DETERMINATION (MODIFIED)
Monitoring station identifiers (6)
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
Named boat-access points from the USGS National Boat Ramps inventory