South Mountain Lake-Cove
South Mountain Lake-Cove in Grafton County, New Hampshire has a water quality grade of B (Good). Phosphorus: 9.7 µg/L. Surface area: 27 acres.
- Area
- 27 acres
- Type
- Oligotrophic
South Mountain Lake-Cove is a 27-acre cold, clear oligotrophic lake in Grafton County, New Hampshire. Water quality is graded B based on 1 sampling years through 2025. Compared to the 26 other monitored lakes in Grafton County, South Mountain Lake-Cove ranks #18 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2025-08-05. Grade methodology: LakeGrade methodology.
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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.
Good for swimming, clear water with low algae levels
Water Quality Grade: B (Good)
No clarity data. Phosphorus level: 9.7 µg/L. Trophic State Index: 37.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 9.7 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 37 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near South Mountain Lake-Cove
Compare lakeside cabins, hotels, and vacation rentals near South Mountain Lake-Cove in Grafton 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 South Mountain Lake-Cove
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Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 27 acres |
No bathymetric survey has been published for South Mountain Lake-Cove, so its depth is not documented here.
Fishing South Mountain Lake-Cove
Reservoir Info (USACE NID)
South Mountain Lake-Cove is a man-made reservoir impounded by the Upper Mountain Lake Dam (completed 1963), built primarily for recreation on the Waterman Brook; earth-type dam, 31 ft tall and 660 ft long.
- Surface area
- 27 ac
- Normal storage
- 325 ac-ft
- Max storage
- 499 ac-ft
- Drainage area
- 3.4 sq mi
- Hazard class
- Low
- Owner
- MOUNTAIN LAKES VILLAGE DISTRICT
Source: USACE National Inventory of Dams, NID ID NH00190 · Operator website · Matched by proximity (0.31 km)
EPA Impairment Status
South Mountain Lake-Cove 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 NHLAK801030505-04 · Official waterbody report · Matched by proximity (0.09 km)
County Ranking
Ranked #18 of 27 lakes in Grafton County
Nearby Lakes in Grafton County
Frequently asked questions about South Mountain Lake-Cove
Where is South Mountain Lake-Cove?
- South Mountain Lake-Cove is a lake in Grafton County, New Hampshire. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for South Mountain Lake-Cove?
- South Mountain Lake-Cove in Grafton County, New Hampshire has a water quality grade of B (Good). Phosphorus: 9.7 µg/L. Surface area: 27 acres.
Is South Mountain Lake-Cove safe to swim in?
- Good for swimming, clear water with low algae levels. South Mountain Lake-Cove has a water quality grade of B (Good). Always check local health department advisories before swimming.
Explore South Mountain Lake-Cove 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 B Lakes in New Hampshire
Oligotrophic Lakes in New Hampshire
Where this data comes from
6 measurements from 1 monitoring station, 2021–2025. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- New Hampshire Department Of Environmental Services (BEACH)
111133006 samples · 2021–2025
Analytical methods
- 10-115-01-1 F ~ LACHAT; Total Phosphorus- Manual persulfate digest
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