Nabnasset Pond
Middlesex County, Massachusetts146 acresView mapDirections
Nutrients and algae sit mid-range for this region.
↓ down from B at the last regrade
- Mesotrophic
- Impaired · Algal growth
- #3 of 11 in the county
- 29 ft max depth
- Public access
- Limited data
Nabnasset Pond in Middlesex County, Massachusetts has a water quality grade of C (Fair). Chlorophyll-a (algae): 5.7 µg/L. Surface area: 146 acres.
- Max depth
- ~29 ft est.
- Area
- 146 acres
- Type
- Mesotrophic
- Chlorophyll-a
- 5.7 µg/L
- Public access
- Yes
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Watch Nabnasset Pond’s letter
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Nabnasset Pond is a 146-acre mesotrophic lake in Middlesex County, Massachusetts with an estimated average depth of about 29 feet. Water quality is graded C based on 1 sampling years through 2017. Limited fish-species data available. Public access is available. Compared to the 10 other monitored lakes in Middlesex County, Nabnasset Pond ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, MassDEP, last sampled 2017-08-24. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLimited data
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The C is nutrients and algae, not a swimming clearance. Nabnasset Pond is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, mercury, nuisance exotic species. Check local advisories before you swim.
Water Quality Grade: C (Fair)
No clarity data. Chlorophyll-a 5.7 µg/L. TSI 48. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | 5.7 µg/L | Fair |
| Trophic State Index (TSI) | 48 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~29 ft est. |
| Average Depth | ~13 ft est. |
| Surface Area | 146 acres |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Massachusetts has not published bathymetry for Nabnasset Pond.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Fishing Nabnasset Pond
Reservoir Info (USACE NID)
Nabnasset Pond is a man-made reservoir impounded by the Nabnasset Pond Dam (completed 1926), built primarily for recreation on the Blue Brook to Stony Brook; earth-type dam, 14 ft tall and 200 ft long.
- Surface area
- 146 ac
- Normal storage
- 961 ac-ft
- Max storage
- 1,454 ac-ft
- Drainage area
- 1.73 sq mi
- Hazard class
- Significant
- Owner
- Town of Westford
Source: USACE National Inventory of Dams, NID ID MA01182 · Operator website
EPA Impairment Status
Nabnasset Pond is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MA84044 · Official waterbody report
County Ranking
Ranked #3 of 11 lakes in Middlesex County
Nearby Lakes in Middlesex County
Frequently asked questions about Nabnasset Pond
Where is Nabnasset Pond?
- Nabnasset Pond is a lake in Middlesex County, Massachusetts. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Nabnasset Pond?
- Nabnasset Pond in Middlesex County, Massachusetts has a water quality grade of C (Fair). Chlorophyll-a (algae): 5.7 µg/L. Surface area: 146 acres.
Is Nabnasset Pond safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Nabnasset Pond is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, mercury, nuisance exotic species. Check local advisories before you swim.
How deep is Nabnasset Pond?
- No published bathymetric survey covers Nabnasset Pond, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 29 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 146 acres.
Explore Nabnasset Pond across LakeQuality
Species activity outlook by water temperature and season
Where to stay at Massachusetts's top lakes, each with its grade
Moderate nutrients, good water quality
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Where this data comes from
3 measurements from 1 monitoring station, 2017. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Massachusetts Department of Environmental Protection (MassDEP)
MASSDEP3 samples · 2017
Analytical methods
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)