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LakeQuality

Data Report · Updated July 2026

The State of Massachusetts’s Lakes 2026

Of 98 monitored lakes in Massachusetts, 63.3% earn a water-quality grade of A or B and 17.3% score D or F (average grade B). Sherman Reservoir is the cleanest;

98
Monitored lakes graded
B
Average grade
63.3%
Grade A or B
0%
On impaired list

Massachusetts grade distribution

A
B
C
F
A: 39 (39.8%)B: 23 (23.5%)C: 19 (19.4%)D: 2 (2.0%)F: 15 (15.3%)

Cleanest lakes in Massachusetts

Highest combined water-quality score, 2026.

  1. 1.ASherman Reservoir — Franklin County10 µg/L P · 2 µg/L chl-a

Most-polluted lakes

Lowest combined water-quality score among monitored lakes.

  1. 1.ASherman Reservoir — Franklin County10 µg/L P · 2 µg/L chl-a

Worst algae hotspots

Highest measured chlorophyll-a (algae) concentration.

  1. 1.FWedge Pond — Middlesex County70 µg/L chlorophyll-a
  2. 2.FBillerica Impoundment Lake — Middlesex County69 µg/L chlorophyll-a
  3. 3.FBarkers Pond — Middlesex County55 µg/L chlorophyll-a
  4. 4.FSantuit 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.FUpper Artichoke Reservoir — Essex County44 µg/L chlorophyll-a
  8. 8.FGleasons Pond — Middlesex County44 µg/L chlorophyll-a
  9. 9.FSouth Watuppa Pond — Bristol County43 µg/L chlorophyll-a
  10. 10.FBartlett Pond — Worcester County38 µg/L chlorophyll-a

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 Secchi clarity, total phosphorus, and chlorophyll-a 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,” lakequality.org/report/ma.