Halfmoon Lake
Halfmoon Lake in Belknap County, New Hampshire is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 14.2 ft visibility.
- Clarity
- 14.2 ft
- Public access
- Yes
Why Halfmoon Lake has no grade
We grade a lake only when its monitoring record clears the evidence bar: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Halfmoon Lake, the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity. Sampling here has recorded water clarity, but not phosphorus and algae (chlorophyll-a).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by your state environmental agency and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Halfmoon Lake is a lake in Belknap County, New Hampshire. Limited fish-species data available. Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2021-07-21. Grade methodology: LakeGrade methodology.
Watch Halfmoon Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Not ratedBacteria advisory
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Halfmoon Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Good clarity, visible to about 14.2 ft. Trophic State Index: 39.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 14.2 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 39 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Halfmoon Lake
Compare lakeside cabins, hotels, and vacation rentals near Halfmoon Lake in Belknap 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 Halfmoon Lake
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Recreation & Access
- Halfmoon LakePublic
Named access points from the USGS National Boat Ramps inventory, snapped within 5 km. More lakes with boat ramps
Fishing Halfmoon Lake
EPA Impairment Status
Halfmoon 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 NHLAK700060402-03 · Official waterbody report
Graded lakes near Halfmoon Lake
Halfmoon Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Belknap County
Frequently asked questions about Halfmoon Lake
Where is Halfmoon Lake?
- Halfmoon Lake is a lake in Belknap County, New Hampshire. LakeQuality has not rated this lake (UNRATED) — there is not enough recent sampling to assign a letter.
What is the water quality grade for Halfmoon Lake?
- Halfmoon Lake in Belknap County, New Hampshire is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 14.2 ft visibility.
Is Halfmoon Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Halfmoon Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
Are there boat ramps on Halfmoon Lake?
- Halfmoon Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Halfmoon Lake. Public access is listed as yes.
Explore Halfmoon 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 Lakes in New Hampshire
Oligotrophic Lakes in New Hampshire
Where this data comes from
6 measurements from 1 monitoring station, 2021. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- North American Lake Management Society
NALMS6 samples · 2021
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
Named boat-access points from the USGS National Boat Ramps inventory