North Mountain Lake-Beach
Grafton County, New Hampshire27 acresView mapDirections
NHDES publishes the water-quality measurements for North Mountain Lake-Beach. Here is what has been measured.
- Impaired · Algal growth
- Limited data
North Mountain Lake-Beach in Grafton County, New Hampshire has water-quality measurements published by NHDES, shown here as reported. Phosphorus: 9.2 µg/L. Surface area: 27 acres.
North Mountain Lake-Beach is a 27-acre lake in Grafton County, New Hampshire.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2025-08-05. Methodology: how these readings are compared.
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. North Mountain Lake-Beach is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, mercury, nutrients (phosphorus, nitrogen), oxygen depletion (low DO), pH / acidity. Check local advisories before you swim.
Whether North Mountain Lake-Beach 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 North Mountain Lake-Beach
These are the measurements NHDES publishes for North Mountain Lake-Beach, 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 9.2 µg/L. TSI 36.
| 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 | 9.2µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | No reading 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. | 36 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about North Mountain Lake-Beach
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Lake Details
Surface area
27 acres
No bathymetric survey has been published for North Mountain Lake-Beach, so its depth is not documented here.
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Fishing North Mountain Lake-Beach
Reservoir Info (USACE NID)
North Mountain Lake-Beach 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 (0.08 km)
EPA Impairment Status
North Mountain Lake-Beach is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
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 NHLAK801030505-03 · Official waterbody report
Nearby Lakes in Grafton County
Frequently asked questions about North Mountain Lake-Beach
Where is North Mountain Lake-Beach?
- North Mountain Lake-Beach 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 North Mountain Lake-Beach?
- North Mountain Lake-Beach in Grafton County, New Hampshire has water-quality measurements published by NHDES, shown here as reported. Phosphorus: 9.2 µg/L. Surface area: 27 acres.
Is North Mountain Lake-Beach safe to swim in?
- Nutrient and algae readings are not a swimming clearance. North Mountain Lake-Beach is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, mercury, nutrients (phosphorus, nitrogen), oxygen depletion (low DO), pH / acidity. Check local advisories before you swim.
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Where this data comes from
2 measurements from 1 monitoring station, 2024–2025. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- New Hampshire Department Of Environmental Services (BEACH)
111133002 samples · 2024–2025
Analytical methods
- 10-115-01-1 F ~ LACHAT; Total Phosphorus- Manual persulfate digest
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