Late afternoon sun over Slim Lake, scattering a bright path across wind-textured water

Middlesex County Lake Quality

Massachusetts, 97 lakes, average grade C (Fair)

Middlesex County has 97 monitored lakes, enough that within-county variation matters as much as the county average. Some are deep glacial basins, others are shallow agricultural-watershed waters, and the measurements reflect that mix. 10 of those lakes carry an A–F grade. The county-level summary describes that subset, not every water body listed. 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 Gleasons Pond (F).

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Quick Answers for Middlesex County

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Planning a trip? Check special fishing regulations for South Reservoir — or check the official Massachusetts fishing regulations.

All Lakes in Middlesex County

97 lakes · 10 graded, 87 not rated10 graded lakes · 87 not rated, hidden

Include not-rated lakes (87)

#	Lake	Grade	Clarity	Phosphorus	Algae	Trophic	Access
1	ASouth ReservoirMiddlesex	A	No recent samples	No recent samples	2.5 µg/L	No recent samples	Not recorded
2	AFitchburg ReservoirMiddlesex	A	No recent samples	No recent samples	2.8 µg/L	No recent samples	Not recorded
3	CNabnasset PondMiddlesex	C	No recent samples	No recent samples	5.7 µg/L	No recent samples	✓ Public
4	CCambridge ReservoirMiddlesex	C	No recent samples	No recent samples	7.4 µg/L	No recent samples	Not recorded
5	DHeart PondMiddlesex	D	No recent samples	No recent samples	14.6 µg/L	No recent samples	Not recorded
6	DBoons PondMiddlesex	D	No recent samples	No recent samples	9.8 µg/L	No recent samples	Not recorded
7	DHorn PondMiddlesex	D	No recent samples	No recent samples	13.4 µg/L	No recent samples	✓ Public
8	FGleasons PondMiddlesex	F	No recent samples	No recent samples	43.9 µg/L	No recent samples	✓ Public
9	FBarkers PondMiddlesex	F	No recent samples	No recent samples	54.5 µg/L	No recent samples	Not recorded
10	FWedge PondMiddlesex	F	No recent samples	No recent samples	70.4 µg/L	No recent samples	Not recorded
	NRFarm PondMiddlesex	NR	19.5 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRSpy PondMiddlesex	NR	5 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRLake QuannapowittMiddlesex	NR	1.3 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRUpper Mystic LakeMiddlesex	NR	No recent samples	28.1 µg/L	No recent samples	No recent samples	✓ Public
	NRLong Pond-Richardson BeachMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBillerica Impoundment LakeMiddlesex	NR	No recent samples	No recent samples	68.6 µg/L	No recent samples	Not recorded
	NRAshby ReservoirMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRHarbor PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRHeald PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRCoon Tree PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRNashua River ReservoirMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRPlow Shop PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NREldridge PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRGrove PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRSandy PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFlannagan PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLong PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRSpectacle PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLong PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	✓ Public
	NRFort PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRNagog PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRCramberry Bog Reservoir Number OneMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRRussell MillpondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBatemans PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRWarners PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRWhite PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFairhaven BayMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFlints PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRWalden PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLower Mystic LakeMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRUpper Mystic LakeMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRNorth ReservoirMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRMiddle ReservoirMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRSpot PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRCrystal LakeMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRMill Pond ReservoirMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRNutting LakeMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRRichardson PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLong PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRAmes PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRMartins PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRSwan PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRPeters PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFlint PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	✓ Public
	NRAlthea LakeMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBurges PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRNewfield PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFletchers PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLong Sought-for PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRKeyes PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRForge PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRWhitney PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLost LakeMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRKnops PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBaddacook PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	✓ Public
	NRMassapoag PondsMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLower Massapoag PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFresh PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRHardys PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRCrystal LakeMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRWeston ReservoirMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRNorumbega ReservoirMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRDug PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBracket Reservoir (Number Two)Middlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRWaushakum PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLake WinthropMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NREcho LakeMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRNorth PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRWhitehall ReservoirMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRAshland ReservoirMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	✓ Public
	NRWilliams LakeMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRHager PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFoss Reservoir (Number Three)Middlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFarm PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLearned PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFisk PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLake CochituateMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRDudley PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRNonesuch PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRHeard PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFarrar PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRWhite PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRPuffer PondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRCarding MillpondMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFort Meadow ReservoirMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFort Meadow ReservoirMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRMillham ReservoirMiddlesex	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded

NR = not rated: there is not enough recent sampling to support a letter. That is EPA Integrated Reporting Category 3 (insufficient information), not a failing grade. How grading works.

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Other Counties in Massachusetts

Franklin County

26 lakes · Avg grade A

Norfolk County

32 lakes · Avg grade A

Berkshire County

72 lakes · Avg grade B

Worcester County

220 lakes · Avg grade B

Barnstable County

94 lakes · Avg grade B

Hampshire County

21 lakes · Avg grade B

See how Middlesex County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all United States (49 states), Canada (Ontario, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador), and 38 other country hubs..

Source: EPA National Aquatic Resource Surveys, 2026.