Sullivan County Lake Quality
New Hampshire, 25 lakes, average grade B (Good)
Sullivan County's 25 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. The county-wide average lands at B — solid water quality with most lakes carrying clear summer transparency and low-to-moderate phosphorus.
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 Ashuelot Pond-Deep Spot (A); the most-stressed is Baptist Pond-Deep Spot (D).
Where to stay near Sullivan County
Top-rated places to stay near Sullivan County
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a trip to Sullivan County?
Get lake water-quality report cards plus the best cabin & lodging deals near Sullivan County — straight to your inbox. No spam, unsubscribe anytime.
Quick Answers for Sullivan County
Planning a trip? Check special fishing regulations for Ashuelot Pond-Deep Spot — or check the official New Hampshire fishing regulations.
All Lakes in Sullivan County
25 lakes · 18 graded, 7 not rated18 graded lakes · 7 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | AAshuelot Pond-Deep SpotSullivan | A | No recent samples | 12.4 µg/L | 3.9 µg/L | No recent samples | Not recorded |
| 2 | ACrescent Lake-Deep SpotSullivan | A | No recent samples | 10.2 µg/L | 3.6 µg/L | No recent samples | Not recorded |
| 3 | AEastman Pond-Deep SpotSullivan | A | No recent samples | 7.6 µg/L | 3 µg/L | No recent samples | Not recorded |
| 4 | ALedge Pond-Deep SpotSullivan | A | No recent samples | 7.6 µg/L | 2.5 µg/L | No recent samples | Not recorded |
| 5 | AMillen Pond-Deep SpotSullivan | A | No recent samples | 8.1 µg/L | 3.1 µg/L | No recent samples | Not recorded |
| 6 | AMountainview Lake-Deep SpotSullivan | A | No recent samples | 10.9 µg/L | 3 µg/L | No recent samples | Not recorded |
| 7 | AOtter Pond-Deep SpotSullivan | A | No recent samples | 9.8 µg/L | 2.5 µg/L | No recent samples | Not recorded |
| 8 | ARand Pond-Deep SpotSullivan | A | No recent samples | 9.4 µg/L | 2.3 µg/L | No recent samples | Not recorded |
| 9 | ARockybound Pond-Deep SpotSullivan | A | No recent samples | 12.2 µg/L | 2.1 µg/L | No recent samples | Not recorded |
| 10 | ASunapee LakeSullivan | A | No recent samples | 5 µg/L | 1.1 µg/L | No recent samples | Not recorded |
| 11 | BBlack River Confluence LakeSullivan | B | No recent samples | 14.2 µg/L | No recent samples | No recent samples | Not recorded |
| 12 | BDutchman Pond-Deep SpotSullivan | B | No recent samples | 9.2 µg/L | 1.8 µg/L | No recent samples | Not recorded |
| 13 | BLong Pond-Deep SpotSullivan | B | No recent samples | 6.6 µg/L | 2.2 µg/L | No recent samples | Not recorded |
| 14 | BMarshall Pond-Deep SpotSullivan | B | No recent samples | 11.4 µg/L | No recent samples | No recent samples | Not recorded |
| 15 | BStocker Pond-Deep SpotSullivan | B | No recent samples | 10 µg/L | 0.8 µg/L | No recent samples | Not recorded |
| 16 | DBaptist Pond-Deep SpotSullivan | D | No recent samples | 14.2 µg/L | 9.4 µg/L | No recent samples | Not recorded |
| 17 | DMill PondSullivan | D | No recent samples | 28.9 µg/L | 4 µg/L | No recent samples | Not recorded |
| 18 | DPerkins Pond-Deep SpotSullivan | D | No recent samples | 9.9 µg/L | 14 µg/L | No recent samples | Not recorded |
| NRDutchman Pond-Hull-SchulmanSullivan | NR | No recent samples | 13.1 µg/L | No recent samples | No recent samples | Not recorded | |
| NRGilman Pond-Deep SpotSullivan | NR | No recent samples | 5 µg/L | 0.6 µg/L | No recent samples | Not recorded | |
| NRHalfmoon Pond-Deep SpotSullivan | NR | No recent samples | 14.6 µg/L | No recent samples | No recent samples | Not recorded | |
| NRKolelemook LakeSullivan | NR | 19.8 ft | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRLake SunapeeSullivan | NR | 26.7 ft | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRMoses Pond-Deep SpotSullivan | NR | No recent samples | 16.9 µg/L | No recent samples | No recent samples | Not recorded | |
| NRPerkins Pond-BurmaSullivan | NR | No recent samples | 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.
Lake Match
Which lake suits how you actually use one?
Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of graded lakes that fit, with the water quality behind each one.
Other Counties in New Hampshire
See how Sullivan 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.