Loon Lake-Deep Spot
Grafton County, New HampshireView mapDirections
NHDES publishes the water-quality measurements for Loon Lake-Deep Spot. Here is what has been measured.
- Mesotrophic
- Impaired · Mercury
- Public access
Loon Lake-Deep Spot in Grafton County, New Hampshire has water-quality measurements published by NHDES, shown here as reported. Phosphorus: 10.8 µg/L. Chlorophyll-a (algae): 4.8 µg/L.
Loon Lake-Deep Spot is a mesotrophic lake in Grafton County, New Hampshire. Limited fish-species data available. Public access is available. Compared to the 26 other monitored lakes in Grafton County, Loon Lake-Deep Spot ranks #10 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2025-08-19. Methodology: how these readings are compared.
Swimming conditions
Readings onlyLow algae
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Loon Lake-Deep Spot is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury, metals (other than mercury), pH / acidity. Check local advisories before you swim.
Whether Loon Lake-Deep Spot is safe to swim in today is a call for the New Hampshire Department of Environmental Services and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Loon Lake-Deep Spot
These are the measurements NHDES publishes for Loon Lake-Deep Spot, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Phosphorus 10.8 µg/L. Chlorophyll-a 4.8 µg/L. TSI 42.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | 10.8µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 4.8µg/L | Measured, not scored The green pigment in algae — a direct measure of how much algae is in the water. |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 42 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Loon Lake-Deep Spot
Answers come straight from the public measurements and survey records on this page.
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Fishing Loon Lake-Deep Spot
EPA Impairment Status
Loon Lake-Deep Spot is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
Designated uses not supporting: Aquatic life, Fish consumption.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit NHLAK700010307-01 · Official waterbody report
Nearby Lakes in Grafton County
Frequently asked questions about Loon Lake-Deep Spot
Where is Loon Lake-Deep Spot?
- Loon Lake-Deep Spot is a lake in Grafton County, New Hampshire. Its water-quality measurements are published by NHDES and shown on this page as reported.
What is the water quality of Loon Lake-Deep Spot?
- Loon Lake-Deep Spot in Grafton County, New Hampshire has water-quality measurements published by NHDES, shown here as reported. Phosphorus: 10.8 µg/L. Chlorophyll-a (algae): 4.8 µg/L.
Is Loon Lake-Deep Spot safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Loon Lake-Deep Spot is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury, metals (other than mercury), pH / acidity. Check local advisories before you swim.
Can I fish at Loon Lake-Deep Spot?
- Public access to Loon Lake-Deep Spot is listed as yes on the lake record. Seasons, size and bag limits, and whether you need a license are set by New Hampshire's fish and wildlife agency, so check its current regulations before you go.
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Where this data comes from
30 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)
1111330030 samples · 2020–2025
Analytical methods
- 10-115-01-1 F ~ LACHAT; Total Phosphorus- Manual persulfate digest
- CHLOROPHYLL A-B-C DETERMINATION (MODIFIED)
Monitoring station identifiers (1)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database