Merrimack County Lake Quality

New Hampshire, 47 lakes, average grade B (Good)

Merrimack County's 47 graded lakes fall in the moderate-density bracket for New Hampshire. The county-level average smooths over real differences — a single agricultural watershed near the southwest corner can pull the average down even if the rest of the county runs clean. With an average grade of B, Merrimack County sits comfortably above the New Hampshire median.

Most of the county's monitored lakes are shallow — under 50 feet — which means wind keeps the water column mixed all summer and sediment-bound phosphorus releases back into the surface layer whenever the bottom is disturbed. Blaisdell Lake-Deep Spot (A) is the cleanest in the county.

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Quick Answers for Merrimack County

Cleanest lakes in Merrimack County →Cleanest lakes in New Hampshire →Safest swimming lakes in New Hampshire →

Planning a trip? Check special fishing regulations for Blaisdell Lake-Deep Spot — or check the official New Hampshire fishing regulations.

All Lakes in Merrimack County

47 lakes · 36 graded, 11 not rated36 graded lakes · 11 not rated, hidden

Include not-rated lakes (11)

#	Lake	Grade	Clarity	Phosphorus	Algae	Trophic	Access
1	ABlaisdell Lake-Deep SpotMerrimack	A	No recent samples	8.2 µg/L	2.8 µg/L	No recent samples	Not recorded
2	AClough Pond-Deep SpotMerrimack	A	No recent samples	15.8 µg/L	3.5 µg/L	No recent samples	Not recorded
3	ACold Pond-Deep SpotMerrimack	A	No recent samples	8.6 µg/L	0.8 µg/L	No recent samples	Not recorded
4	AHighland Lake-Deep SpotMerrimack	A	No recent samples	13.1 µg/L	3.5 µg/L	No recent samples	Not recorded
5	ALake Massasecum-Deep SpotMerrimack	A	No recent samples	9.6 µg/L	3.2 µg/L	No recent samples	Not recorded
6	ALake Winnepocket-Deep SpotMerrimack	A	No recent samples	8.1 µg/L	3.2 µg/L	No recent samples	Not recorded
7	BBear Hill Pond-Deep SpotMerrimack	B	No recent samples	7.4 µg/L	No recent samples	No recent samples	Not recorded
8	BBradley Lake-Deep SpotMerrimack	B	No recent samples	5.6 µg/L	No recent samples	No recent samples	Not recorded
9	BChalk Pond-Main BeachMerrimack	B	No recent samples	5.7 µg/L	No recent samples	No recent samples	Not recorded
10	BChase Pond-Deep SpotMerrimack	B	No recent samples	12.6 µg/L	4.2 µg/L	No recent samples	Not recorded
11	BChestnut Pond-Deep SpotMerrimack	B	No recent samples	10 µg/L	4.3 µg/L	No recent samples	Not recorded
12	BKnowles Pond-Deep SpotMerrimack	B	No recent samples	8 µg/L	2.8 µg/L	No recent samples	Not recorded
13	BLake Winnepocket-Austin PointMerrimack	B	No recent samples	5.2 µg/L	No recent samples	No recent samples	Not recorded
14	BLake Winnepocket-CogswellMerrimack	B	No recent samples	6.1 µg/L	No recent samples	No recent samples	Not recorded
15	BLake Winnepocket-Dawe PointMerrimack	B	No recent samples	5.5 µg/L	No recent samples	No recent samples	Not recorded
16	BLake Winnepocket-Pratt CoveMerrimack	B	No recent samples	5.6 µg/L	No recent samples	No recent samples	Not recorded
17	BLake Winnepocket-West Wind VillageMerrimack	B	No recent samples	6.1 µg/L	No recent samples	No recent samples	Not recorded
18	BPillsbury Lake-Deep SpotMerrimack	B	No recent samples	13.8 µg/L	No recent samples	No recent samples	Not recorded
19	BPleasant Lake-OutletMerrimack	B	No recent samples	5 µg/L	No recent samples	No recent samples	Not recorded
20	BPleasant Lake-Southeast CoveMerrimack	B	No recent samples	5 µg/L	No recent samples	No recent samples	Not recorded
21	BWaukeena Lake-Deep SpotMerrimack	B	No recent samples	10 µg/L	3.5 µg/L	No recent samples	Not recorded
22	CChalk Pond-Deep SpotMerrimack	C	No recent samples	9.7 µg/L	4.9 µg/L	No recent samples	Not recorded
23	CClement Pond-Deep SpotMerrimack	C	No recent samples	11.1 µg/L	5.1 µg/L	No recent samples	Not recorded
24	CHighland Lake-OutletMerrimack	C	No recent samples	16.6 µg/L	No recent samples	No recent samples	Not recorded
25	CHothole Pond-Deep SpotMerrimack	C	No recent samples	16.4 µg/L	5.9 µg/L	No recent samples	Not recorded
26	CKezar Lake-Deep SpotMerrimack	C	No recent samples	22.6 µg/L	3.4 µg/L	No recent samples	Not recorded
27	CLyford Pond-Deep SpotMerrimack	C	No recent samples	18 µg/L	No recent samples	No recent samples	Not recorded
28	CMesser Pond-Deep SpotMerrimack	C	No recent samples	16.8 µg/L	3.6 µg/L	No recent samples	Not recorded
29	CNew Pond-Deep SpotMerrimack	C	No recent samples	14.4 µg/L	4.7 µg/L	No recent samples	Not recorded
30	CRussell Pond-Deep SpotMerrimack	C	No recent samples	19.1 µg/L	No recent samples	No recent samples	Not recorded
31	CSucker Brook LakeMerrimack	C	No recent samples	18.6 µg/L	No recent samples	No recent samples	Not recorded
32	CTodd Lake-Deep SpotMerrimack	C	No recent samples	15.8 µg/L	4.7 µg/L	No recent samples	Not recorded
33	CTom Pond-Deep SpotMerrimack	C	No recent samples	13.1 µg/L	7.8 µg/L	No recent samples	Not recorded
34	CTuree Pond-Deep SpotMerrimack	C	No recent samples	19.5 µg/L	4.3 µg/L	No recent samples	Not recorded
35	CTuree Pond-Firehouse Pond OutletMerrimack	C	No recent samples	18.2 µg/L	No recent samples	No recent samples	Not recorded
36	CWebster Lake-Deep SpotMerrimack	C	No recent samples	17.6 µg/L	3.3 µg/L	No recent samples	Not recorded
	NRChalk Pond-South BeachMerrimack	NR	No recent samples	7.5 µg/L	No recent samples	No recent samples	Not recorded
	NRCole Pond-BeachMerrimack	NR	No recent samples	9.9 µg/L	No recent samples	No recent samples	Not recorded
	NRCraney Pond-Deep SpotMerrimack	NR	No recent samples	16.3 µg/L	6.5 µg/L	No recent samples	Not recorded
	NRGiles Pond-Deep SpotMerrimack	NR	No recent samples	13.4 µg/L	5.2 µg/L	No recent samples	Not recorded
	NRLake Massasecum-GenericMerrimack	NR	No recent samples	9 µg/L	No recent samples	No recent samples	Not recorded
	NRLake Winnepocket-Agoos ShoreMerrimack	NR	No recent samples	6.3 µg/L	No recent samples	No recent samples	Not recorded
	NRLake Winnepocket-End of Lake InletMerrimack	NR	No recent samples	7.7 µg/L	No recent samples	No recent samples	Not recorded
	NRRolf Pond-Deep SpotMerrimack	NR	No recent samples	12.3 µg/L	No recent samples	No recent samples	Not recorded
	NRSuncook River LakeMerrimack	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRTucker PondMerrimack	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRWalker PondMerrimack	NR	10.4 ft	No recent samples	No recent samples	No recent samples	Not recorded

NR = not rated: the monitoring record does not meet the evidence bar for a grade. That is EPA Integrated Reporting Category 3 (insufficient information), not a failing grade. How grading works.

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Other Counties in New Hampshire

Carroll County

22 lakes · Avg grade B

Sullivan County

25 lakes · Avg grade B

Grafton County

35 lakes · Avg grade B

Strafford County

16 lakes · Avg grade B

Coos County

15 lakes · Avg grade B

Cheshire County

39 lakes · Avg grade B

See how Merrimack County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 49 states and 2 Canadian provinces.

Source: EPA National Aquatic Resource Surveys, 2026.