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LakeQuality
Pink and orange afterglow over the treeline on Slim Lake after sunset

Updated August 2026

The State of Massachusetts's Lakes 2026

Of 103 lakes in Massachusetts, 50.6% earn a water-quality grade of A or B and 30.9% score D or F (average grade B). 98 lakes (95.1%) are on an official impaired-waters list.

Data Report

103
Monitored lakes graded
B
Average grade
50.6%
Grade A or B
95.1%
On impaired list

Massachusetts grade distribution

A
C
D
F
A: 37 (45.7%)B: 4 (4.9%)C: 15 (18.5%)D: 16 (19.8%)F: 9 (11.1%)

Cleanest lakes in Massachusetts

Highest combined water-quality score, 2026.

No qualifying lakes with sufficient data.

Most-polluted lakes

Lowest combined water-quality score among monitored lakes.

No qualifying lakes with sufficient data.

Worst algae hotspots

Highest measured chlorophyll-a (algae) concentration.

  1. 1.FWedge Pond — Middlesex County70 µg/L chlorophyll-a
  2. 2.NRBillerica Impoundment Lake — Middlesex County69 µg/L chlorophyll-a
  3. 3.FBarkers Pond — Middlesex County55 µg/L chlorophyll-a
  4. 4.NRSantuit Pond — Barnstable County52 µg/L chlorophyll-a
  5. 5.FCooks Pond — Plymouth County48 µg/L chlorophyll-a
  6. 6.FFurnace Pond — Plymouth County47 µg/L chlorophyll-a
  7. 7.FGleasons Pond — Middlesex County44 µg/L chlorophyll-a
  8. 8.FSouth Watuppa Pond — Bristol County43 µg/L chlorophyll-a
  9. 9.FBartlett Pond — Worcester County38 µg/L chlorophyll-a
  10. 10.FNashawannuck Pond — Hampshire County32 µg/L chlorophyll-a

Trending lakes

Improving

  1. 1.AEzekiel Pond — Plymouth County
  2. 2.DMonponsett Pond — Plymouth County
  3. 3.NRSnows Pond — Plymouth County
  4. 4.NRUpper Mystic Lake — Middlesex County
  5. 5.NRWhite Island Pond — Plymouth County

Declining

  1. 1.DLower Spectacle Pond — Berkshire County
  2. 2.CBuckley-Dunton Lake — Berkshire County
  3. 3.ALong Pond — Barnstable County
  4. 4.NRFarm Pond — Middlesex County
  5. 5.NRSpy Pond — Middlesex County
  6. 6.NRWachusett Reservoir — Worcester County
  7. 7.NRSantuit Pond — Barnstable County
  8. 8.NRWhite Oak Brook Lake — Plymouth County

Impaired waters in Massachusetts

98 lakes appear on the EPA/state 303(d) impaired-waters list (61 formally listed, 32 with a cleanup plan/TMDL).

Algal growth · 49Mercury · 43Nuisance exotic species · 40Oxygen depletion (low DO) · 26Nutrients (phosphorus, nitrogen) · 22Noxious aquatic plants · 16Turbidity · 10Habitat alterations · 9

Explore Massachusetts lakes

Lake Fishing Forecast

Species activity outlook by water temperature and season

Massachusetts Lake Trips

Where to stay at Massachusetts's top lakes, each with its grade

Grades combine total phosphorus, total nitrogen, chlorophyll-a, and turbidity from the EPA Water Quality Portal and state agencies. See the full methodology, the national State of America’s Lakes report, or all Massachusetts lakes.

Cite this report: LakeQuality, “The State of Massachusetts's Lakes 2026”.