Middlesex County Lake Quality
Massachusetts, 14 lakes, average grade C (Fair)
Only 14 lakes in Middlesex County carry an active grade. The county-level summary is therefore representative of those specific lakes, not necessarily of every water body in the county. Middlesex County averages to a C. The distribution behind that average matters more than the letter: a few stressed lakes versus many decent ones can produce the same average as the inverse.
The county's lakes lean shallow, which makes the grades sensitive to wind, sediment-resuspension, and any nutrient inputs from the watershed. The cleanest lake on the books is South Reservoir (A); the most-stressed is Long Pond-Richardson Beach (F).
Quick Answers for Middlesex County
Planning a trip? Check special fishing regulations for South Reservoir — or check the official Massachusetts fishing regulations.
All Lakes in Middlesex County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | South Reservoir | A | - | - |
| 2 | Fitchburg Reservoir | A | - | - |
| 3 | Upper Mystic Lake | B | - | 28.2 µg/L |
| 4 | Cambridge Reservoir | B | - | - |
| 5 | Nabnasset Pond | B | - | - |
| 6 | Boons Pond | B | - | - |
| 7 | Heart Pond | C | - | - |
| 8 | Horn Pond | C | - | - |
| 9 | Long Pond-Richardson Beach | F | - | 1230 µg/L |
| 10 | Billerica Impoundment Lake | F | - | - |
| 11 | Gleasons Pond | F | - | - |
| 12 | Barkers Pond | F | - | - |
| 13 | Spy Pond | F | - | - |
| 14 | Wedge Pond | F | - | - |
Other Counties in Massachusetts
See how Middlesex County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 36 states.
Where to stay near Middlesex County
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Source: EPA National Aquatic Resource Surveys, 2026.