Long Pond-Deep Spot
Sullivan County, New Hampshire120 acresView mapDirections
NHDES publishes the water-quality measurements for Long Pond-Deep Spot. Here is what has been measured.
- Oligotrophic
- Impaired · Mercury
- Public access
Long Pond-Deep Spot in Sullivan County, New Hampshire has water-quality measurements published by NHDES, shown here as reported. Phosphorus: 6.6 µg/L. Chlorophyll-a (algae): 2.2 µg/L. Surface area: 120 acres.
Long Pond-Deep Spot is a 120-acre cold, clear oligotrophic lake in Sullivan County, New Hampshire. Limited fish-species data available. Public access is available. Compared to the 23 other monitored lakes in Sullivan County, Long Pond-Deep Spot ranks #13 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2025-08-26. 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. Long Pond-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 Long Pond-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 Long Pond-Deep Spot
These are the measurements NHDES publishes for Long Pond-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 6.6 µg/L. Chlorophyll-a 2.2 µg/L. TSI 35.
| 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 | 6.6µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 2.2µg/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. | 35 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Long Pond-Deep Spot
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
120 acres
Public access
Yes
Listed by NHDES
No bathymetric survey has been published for Long Pond-Deep Spot, so its depth is not documented here.
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Fishing Long Pond-Deep Spot
Reservoir Info (USACE NID)
Long Pond-Deep Spot is a man-made reservoir impounded by the Long Pond Dam (completed 1910), built primarily for recreation on the Tr Ashuelot River; concrete-type dam, 10 ft tall and 260 ft long.
- Surface area
- 120 ac
- Normal storage
- 238 ac-ft
- Max storage
- 578 ac-ft
- Drainage area
- 1.44 sq mi
- Hazard class
- Low
- Owner
- TOWN OF LEMPSTER
Source: USACE National Inventory of Dams, NID ID NH00271 · Operator website · Matched by proximity (0.49 km)
EPA Impairment Status
Long Pond-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 NHLAK802010101-04 · Official waterbody report
Nearby Lakes in Sullivan County
Frequently asked questions about Long Pond-Deep Spot
Where is Long Pond-Deep Spot?
- Long Pond-Deep Spot is a lake in Sullivan County, New Hampshire. Its water-quality measurements are published by NHDES and shown on this page as reported.
What is the water quality of Long Pond-Deep Spot?
- Long Pond-Deep Spot in Sullivan County, New Hampshire has water-quality measurements published by NHDES, shown here as reported. Phosphorus: 6.6 µg/L. Chlorophyll-a (algae): 2.2 µg/L. Surface area: 120 acres.
Is Long Pond-Deep Spot safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Long Pond-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 Long Pond-Deep Spot?
- Public access to Long Pond-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
22 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)
1111330022 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