Broad Bay-Deep Spot Lake
Carroll County, New HampshireView mapDirections
NHDES publishes the water-quality measurements for Broad Bay-Deep Spot Lake. Here is what has been measured.
- Mesotrophic
- Impaired · Mercury
Broad Bay-Deep Spot Lake in Carroll County, New Hampshire has water-quality measurements published by NHDES, shown here as reported. Phosphorus: 6.8 µg/L. Chlorophyll-a (algae): 2.2 µg/L.
Broad Bay-Deep Spot Lake is a mesotrophic lake in Carroll County, New Hampshire. Compared to the 19 other monitored lakes in Carroll County, Broad Bay-Deep Spot Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2025-08-13. 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. Broad Bay-Deep Spot Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury, nuisance exotic species, pH / acidity. Check local advisories before you swim.
Whether Broad Bay-Deep Spot Lake 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 Broad Bay-Deep Spot Lake
These are the measurements NHDES publishes for Broad Bay-Deep Spot Lake, 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 6.8 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 | 6.8µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 2.2µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 35 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
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Fishing Broad Bay-Deep Spot Lake
EPA Impairment Status
Broad Bay-Deep Spot Lake 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 NHLAK600020804-01-03 · Official waterbody report
Nearby Lakes in Carroll County
Frequently asked questions about Broad Bay-Deep Spot Lake
Where is Broad Bay-Deep Spot Lake?
- Broad Bay-Deep Spot Lake is a lake in Carroll County, New Hampshire. Its water-quality measurements are published by NHDES and shown on this page as reported.
What is the water quality of Broad Bay-Deep Spot Lake?
- Broad Bay-Deep Spot Lake in Carroll County, New Hampshire has water-quality measurements published by NHDES, shown here as reported. Phosphorus: 6.8 µg/L. Chlorophyll-a (algae): 2.2 µg/L.
Is Broad Bay-Deep Spot Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Broad Bay-Deep Spot Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury, nuisance exotic species, pH / acidity. Check local advisories before you swim.
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Where this data comes from
90 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)
1111330090 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