Lake Winnepocket-Cogswell
Lake Winnepocket-Cogswell in Merrimack County, New Hampshire has a water quality grade of B (Good). Phosphorus: 6.1 µg/L.
- Type
- Oligotrophic
Lake Winnepocket-Cogswell is a cold, clear oligotrophic lake in Merrimack County, New Hampshire. Water quality is graded B based on 1 sampling years through 2025. Compared to the 40 other monitored lakes in Merrimack County, Lake Winnepocket-Cogswell ranks #12 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2025-06-02. 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: 6.1 µg/L. Trophic State Index: 30.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 6.1 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 30 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Lake Winnepocket-Cogswell
Compare lakeside cabins, hotels, and vacation rentals near Lake Winnepocket-Cogswell in Merrimack 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 Lake Winnepocket-Cogswell
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Fishing Lake Winnepocket-Cogswell
EPA Impairment Status
Lake Winnepocket-Cogswell is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit NHLAK700030304-08 · Official waterbody report · Matched by proximity (0.73 km)
County Ranking
Ranked #12 of 41 lakes in Merrimack County
Nearby Lakes in Merrimack County
Frequently asked questions about Lake Winnepocket-Cogswell
Where is Lake Winnepocket-Cogswell?
- Lake Winnepocket-Cogswell is a lake in Merrimack 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 Lake Winnepocket-Cogswell?
- Lake Winnepocket-Cogswell in Merrimack County, New Hampshire has a water quality grade of B (Good). Phosphorus: 6.1 µg/L.
Is Lake Winnepocket-Cogswell safe to swim in?
- Good for swimming, clear water with low algae levels. Lake Winnepocket-Cogswell has a water quality grade of B (Good). Always check local health department advisories before swimming.
Explore Lake Winnepocket-Cogswell 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
Hillsborough County · Good
Hillsborough County · Good
Hillsborough County · Good
Hillsborough County · Good
Belknap County · Good
Hillsborough County · Good
Oligotrophic Lakes in New Hampshire
Where this data comes from
7 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- New Hampshire Department Of Environmental Services (BEACH)
111133007 samples · 2020–2025
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