Lake Monomonac-Coot Bay
Cheshire County, New Hampshire18 acresView mapDirections
NHDES publishes the water-quality measurements for Lake Monomonac-Coot Bay. Here is what has been measured.
- Eutrophic
- Impaired · Algal growth
- Limited data
Lake Monomonac-Coot Bay in Cheshire County, New Hampshire has water-quality measurements published by NHDES, shown here as reported. Phosphorus: 40.3 µg/L. Surface area: 18 acres.
Lake Monomonac-Coot Bay is a 18-acre productive, nutrient-rich eutrophic lake in Cheshire County, New Hampshire. Compared to the 37 other monitored lakes in Cheshire County, Lake Monomonac-Coot Bay ranks #38 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2025-07-15. Methodology: how these readings are compared.
Swimming conditions
Readings onlyBacteria advisory
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. Lake Monomonac-Coot Bay is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, biotoxins, mercury, nuisance exotic species, nutrients (phosphorus, nitrogen), pH / acidity. Check local advisories before you swim.
Whether Lake Monomonac-Coot Bay 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 Lake Monomonac-Coot Bay
These are the measurements NHDES publishes for Lake Monomonac-Coot Bay, 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 40.3 µg/L. TSI 57.
| 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 | 40.3µg/L | Poor GoodFairPoor |
| 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. | 57 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Lake Monomonac-Coot Bay
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
18 acres
No bathymetric survey has been published for Lake Monomonac-Coot Bay, so its depth is not documented here.
Stays via Stay22
Stays near Lake Monomonac-Coot Bay
Compare lakeside cabins, hotels, and vacation rentals near Lake Monomonac-Coot Bay in Cheshire 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. The water-quality readings cover nutrients and algae, not lodging. Cabins and rentals around Lake Monomonac-Coot Bay are listed below.
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Fishing Lake Monomonac-Coot Bay
Reservoir Info (USACE NID)
Lake Monomonac-Coot Bay is a man-made reservoir impounded by the Van Dyke Dam (completed 1982), built primarily for recreation on the Monomonac Brook; earth-type dam, 8 ft tall and 94 ft long.
- Surface area
- 18 ac
- Normal storage
- 39 ac-ft
- Max storage
- 66 ac-ft
- Drainage area
- 2.76 sq mi
- Hazard class
- Low
- Owner
- MS KATHLEEN VANDYKE EXECUTOR
Source: USACE National Inventory of Dams, NID ID NH00853 · Operator website · Matched by proximity (0.36 km)
EPA Impairment Status
Lake Monomonac-Coot Bay 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, Recreation.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit NHLAK802020103-06 · Official waterbody report
Nearby Lakes in Cheshire County
Frequently asked questions about Lake Monomonac-Coot Bay
Where is Lake Monomonac-Coot Bay?
- Lake Monomonac-Coot Bay is a lake in Cheshire County, New Hampshire. Its water-quality measurements are published by NHDES and shown on this page as reported.
What is the water quality of Lake Monomonac-Coot Bay?
- Lake Monomonac-Coot Bay in Cheshire County, New Hampshire has water-quality measurements published by NHDES, shown here as reported. Phosphorus: 40.3 µg/L. Surface area: 18 acres.
Is Lake Monomonac-Coot Bay safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Lake Monomonac-Coot Bay is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, biotoxins, mercury, nuisance exotic species, nutrients (phosphorus, nitrogen), pH / acidity. Check local advisories before you swim.
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Where this data comes from
7 measurements from 1 monitoring station, 2023–2025. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- New Hampshire Department Of Environmental Services (BEACH)
111133007 samples · 2023–2025
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