Updated August 2026
Cleanest Lakes by Water Quality
The top 50 U.S. lakes ranked by complete nutrient-and-algae grade. Letters use EPA National Lakes Assessment 2022 ecoregion classes. Secchi depth breaks ties among lakes that share a score — it is shown, not folded into the letter. Limited-data grades are excluded.
Across 5,696 graded lakes in 36 states (9,514 monitored), 20% earn an A and 51% earn an A or B. Not Rated is insufficient evidence, not a failing grade. The top 50 below draw from 6 states, led by Minnesota with 29 — deep, low-nutrient northern waters like Minnesota's Boundary Waters lakes and Wisconsin's spring-fed Northwoods lakes are over-represented at the top.
The cleanest lake on the index is Sunset Lake in Rutland County, VT — Grade A, with 36.1 feet of water clarity and phosphorus of 8.5 µg/L. Below that, the rest of the top 10 span 9.6 feet of Secchi between #1 and #10.
All grades come from EPA National Aquatic Resource Surveys and state monitoring programs (MN PCA, WI DNR). Lakes with fewer than three sampling visits are flagged as "limited data." Water-quality grades describe ecology — they do not replace beach-specific E. coli advisories, which your state health department updates separately.
Top 9 Cleanest Lakes
| Rank | Lake | County | State | Grade | Clarity | Max Depth |
|---|---|---|---|---|---|---|
| 1 | Sunset Lake | Rutland | VT | A | 36.1 ft | - |
| 2 | Flaming Gorge Reservoir | Daggett | UT | A | 31.8 ft | - |
| 3 | Caspian Lake | Orleans | VT | A | 29.5 ft | - |
| 4 | Clearwater Lake | Cook | MN | A | 29 ft | 65 ft |
| 5 | Shadow Lake | Orleans | VT | A | 28.9 ft | - |
| 6 | Maidstone Lake | Essex | VT | A | 28.5 ft | - |
| 7 | Lake Willoughby | Orleans | VT | A | 28.2 ft | - |
| 8 | Holland Lake | Dakota | MN | A | 27.9 ft | 55 ft |
| 9 | Kerbs Lake | Otter Tail | MN | A | 27.7 ft | - |
| 10 | Little Mcdonald Lake | Otter Tail | MN | A | 26.5 ft | 109 ft |
| 11 | Lake Elligo | Orleans | VT | A | 26.2 ft | - |
| 12 | Forest Lake | Washington | VT | A | 25.6 ft | - |
| 13 | Bad Medicine Lake | Becker | MN | A | 25 ft | 84 ft |
| 14 | Serpent Lake | Crow Wing | MN | A | 25 ft | 65 ft |
| 15 | Big Cormorant Lake | Becker | MN | A | 24.8 ft | 75 ft |
| 16 | Seymour Lake | Orleans | VT | A | 24.6 ft | - |
| 17 | Echo Lake | Rutland | VT | A | 24.3 ft | - |
| 18 | Lake Bomoseen | Rutland | VT | A | 23.6 ft | - |
| 19 | Big Sand Lake | Hubbard | MN | A | 23 ft | 135 ft |
| 20 | Stony Lake | Cass | MN | A | 23 ft | 50 ft |
| 21 | Echo Lake | Orleans | VT | A | 23 ft | - |
| 22 | Turtle Lake | Becker | MN | A | 23 ft | 73 ft |
| 23 | Belle Taine Lake | Hubbard | MN | A | 22.8 ft | 56 ft |
| 24 | Eagle Lake | Otter Tail | MN | A | 22.6 ft | 46 ft |
| 25 | Whitefish Lake | Flathead | MT | A | 22 ft | - |
| 26 | West Sylvia Lake | Wright | MN | A | 22 ft | 97 ft |
| 27 | Berlin Pond | Washington | VT | A | 21.7 ft | - |
| 28 | Lake Fairlee | Orange | VT | A | 21.7 ft | - |
| 29 | Long Lake | Cass | MN | A | 21.5 ft | 115 ft |
| 30 | Lake Mirror | Washington | VT | A | 21.3 ft | - |
| 31 | Round Lake | Sawyer | WI | A | 21.1 ft | 74 ft |
| 32 | Bearskin Lake | Cook | MN | A | 21 ft | 78 ft |
| 33 | Six Lake | Otter Tail | MN | A | 21 ft | 140 ft |
| 34 | East Sylvia Lake | Wright | MN | A | 21 ft | 78 ft |
| 35 | Harveys Lake | Caledonia | VT | A | 21 ft | - |
| 36 | Geneva Lake | Walworth | WI | A | 21 ft | 135 ft |
| 37 | Swenson Lake | Beltrami | MN | A | 20.7 ft | 76 ft |
| 38 | Mayhew Lake | Cook | MN | A | 20.6 ft | 84 ft |
| 39 | Long Lake | Clearwater | MN | A | 20.5 ft | 80 ft |
| 40 | Ten Mile Lake | Cass | MN | A | 20.5 ft | 208 ft |
| 41 | Newark Pond | Caledonia | VT | A | 20.4 ft | - |
| 42 | Beaver Lake | Carroll | AR | A | 20.3 ft | - |
| 43 | Gilmore Lake | Hubbard | MN | A | 20.3 ft | 54 ft |
| 44 | Little Sand Lake | Hubbard | MN | A | 20 ft | 80 ft |
| 45 | Long Lake | Beltrami | MN | A | 20 ft | 87 ft |
| 46 | Big Fish Lake | Stearns | MN | A | 20 ft | 70 ft |
| 47 | Ossawinnamakee Lake | Crow Wing | MN | A | 20 ft | 63 ft |
| 48 | Scalp Lake | Otter Tail | MN | A | 20 ft | 90 ft |
| 49 | Sybil Lake | Otter Tail | MN | A | 20 ft | 74 ft |
| 50 | Squaw Smith Lake | Beltrami | MN | A | 20 ft | - |
Where to stay near America's cleanest lakes
Planning a lake trip? Jump to live cabin, resort, and hotel availability on each top-ranked lake's page.
- Sunset Lake · Rutland CountyCabins & hotels near Sunset Lake →
- Flaming Gorge Reservoir · Daggett CountyCabins & hotels near Flaming Gorge Reservoir →
- Caspian Lake · Orleans CountyCabins & hotels near Caspian Lake →
- Clearwater Lake · Cook CountyCabins & hotels near Clearwater Lake →
- Shadow Lake · Orleans CountyCabins & hotels near Shadow Lake →
Top 500 Cleanest Lakes — Water Quality Dataset (2026)
The 500 highest-graded lakes across 36 states in one spreadsheet — A–F grade, water clarity, phosphorus, chlorophyll-a, trophic state, size, public access, and a link to each lake's report card.
Frequently Asked Questions
Sunset Lake in Rutland County, VT, is the highest-rated lake on our index with a Grade A for overall water quality. Its water clarity (Secchi depth) reads 36.1 feet, with phosphorus at 8.5 µg/L.
Lakes earn a letter grade A–F on nutrients and algae — total phosphorus and chlorophyll-a — scored against EPA National Lakes Assessment 2022 ecoregion condition classes. Water clarity (Secchi depth in feet) is measured and shown; it is not the letter. An A is not a swim clearance. Limited-data grades cannot headline this table.
Of 5,696 graded lakes across our 36-state database (9,514 monitored; the rest are Not Rated), 1,140 (20%) earn an A. Another 1,752 earn a B, bringing A-or-B lakes to 2,892 (51% of graded).
Not always. Water clarity correlates with low algae and low phosphorus — the same factors that drive harmful algal blooms — but Secchi does not measure E. coli, cyanotoxins, or a posted beach closure. The letter grade is nutrients and algae, not a same-day clearance. Always check current swimming advisories before getting in.
Clean lakes share three traits: low nutrient inputs (especially phosphorus from septic, fertilizer, and farm runoff), good circulation and depth (deeper lakes resist warming and stratification), and protected forested shorelines that filter runoff. The cleanest lakes on this list tend to be deep, far from cropland, and surrounded by undeveloped land.
More on clean water
The cleanest and dirtiest U.S. lakes in the monitoring record, ranked on EPA nutrient and algae condition classes across thousands of graded lakes.
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.
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.
The cleanest U.S. lakes under 500 acres, ranked on measured nutrients, algae, and water clarity — with the size cutoff applied to the lake, not the sample.