Updated Aug 2026
Maine Lake Water Quality
Water quality grades for 18 monitored lakes across 4 counties.
Maine has 18 graded lakes in our dataset, sampled across 4 counties, drawing on monitoring by the Maine Department of Environmental Protection plus federal and volunteer measurements. Roughly 89% of the state's graded lakes carry an A — 16 lakes that earn the top bracket on the combined Secchi/phosphorus/chlorophyll-a rubric. That share is high by national standards and reflects the depth and natural clarity of glacial lakes in the region.
Most Maine lakes sit in the mesotrophic band — moderate productivity, decent clarity, capable of supporting both warm-water and cool-water fisheries. This is the band where well-managed working lakes tend to land. Washington ranks highest on average county grade (A). Washington sits lowest. With only 4 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.
Grade Distribution
All 18 Maine lakes in the index: 16 (88.9%) carry an A–F grade and 2 (11.1%) are not rated, because they lack enough recent nutrient or algae sampling to support a letter.
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Top-Graded Maine Lakes
The highest water-quality grades in Maine — clarity, depth, and A-F grade at a glance.
Lake Map
Maine reports, fishing & travel
Maine Fishing & Recreation
Licenses, regulations, records, and where to fish across Maine.
Counties
All 4 Maine counties, ranked by average lake water quality. Compare them against every county nationwide in the county rankings, browse the full directory of graded lakes, or pick a different state.
Cleanest Maine Lakes
16 lakes16 graded lakes
| # | Lake | County | Grade | Clarity | Trophic | Access |
|---|---|---|---|---|---|---|
| 1 | ABig Lake | Washington | A | 16.7 ft | Mesotrophic | Not recorded |
| 2 | AEast Musquash Lake | Washington | A | 20.5 ft | Mesotrophic | Not recorded |
| 3 | AGrand Falls Flowage Lake | Washington | A | 14 ft | Mesotrophic | Not recorded |
| 4 | AJunior Lake | Penobscot | A | 25.9 ft | Oligotrophic | Not recorded |
| 5 | AKillman Pond | Hancock | A | 12.7 ft | Mesotrophic | Not recorded |
| 6 | ALewey Lake | Washington | A | 15 ft | Mesotrophic | Not recorded |
| 7 | ALong Lake | Washington | A | 15.6 ft | Mesotrophic | Not recorded |
| 8 | AMiddle Chain Lake | Hancock | A | 14.1 ft | Mesotrophic | Not recorded |
| 9 | APleasant Lake | Washington | A | 27.2 ft | Oligotrophic | Not recorded |
| 10 | APocumcus Lake | Washington | A | 27.9 ft | Oligotrophic | Not recorded |
| 11 | AScraggly Lake | Washington | A | 19.4 ft | Mesotrophic | Not recorded |
| 12 | ASide Pistol Lake | Hancock | A | 16.7 ft | Mesotrophic | Not recorded |
| 13 | ASysladobsis Lake | Washington | A | 27.8 ft | Oligotrophic | Not recorded |
| 14 | AUpper Chain Lake | Hancock | A | 14.5 ft | Mesotrophic | Not recorded |
| 15 | AWest Grand Lake | Washington | A | 36.7 ft | Oligotrophic | Not recorded |
| 16 | AWest Musquash Lake | Washington | A | 31 ft | Oligotrophic | Not recorded |
Maine Lakes Needing Attention
16 lakes16 graded lakes
| # | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | AWest Musquash Lake | Washington | A | 31 ft |
| 2 | AWest Grand Lake | Washington | A | 36.7 ft |
| 3 | AUpper Chain Lake | Hancock | A | 14.5 ft |
| 4 | ASysladobsis Lake | Washington | A | 27.8 ft |
| 5 | ASide Pistol Lake | Hancock | A | 16.7 ft |
| 6 | AScraggly Lake | Washington | A | 19.4 ft |
| 7 | APocumcus Lake | Washington | A | 27.9 ft |
| 8 | APleasant Lake | Washington | A | 27.2 ft |
| 9 | AMiddle Chain Lake | Hancock | A | 14.1 ft |
| 10 | ALong Lake | Washington | A | 15.6 ft |
| 11 | ALewey Lake | Washington | A | 15 ft |
| 12 | AKillman Pond | Hancock | A | 12.7 ft |
| 13 | AJunior Lake | Penobscot | A | 25.9 ft |
| 14 | AGrand Falls Flowage Lake | Washington | A | 14 ft |
| 15 | AEast Musquash Lake | Washington | A | 20.5 ft |
| 16 | ABig Lake | Washington | A | 16.7 ft |
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.
Source: EPA National Aquatic Resource Surveys and the EPA Water Quality Portal.
More on lake water quality
The top-graded lake in every state we cover, picked grade-first with water clarity as the tie-breaker — plus the states whose winner is still not clean.
State-by-state Secchi champions: the clearest measured lake in each U.S. state we grade, which is not the same as the cleanest nutrient grade.
A data snapshot of the lakes we grade: how the A–F distribution breaks down, the clearest and the greenest states, and where the water is improving.
How lakes are graded A–F on nutrients and algae using EPA ecoregion condition classes, what each letter means in the water, and why an A is not a clearance.