Cleanest Lakes by Water Quality

The top 50 lakes ranked by overall water quality grade. Grades are based on water clarity (Secchi depth in feet), phosphorus levels, and chlorophyll-a (algae) concentration using Metropolitan Council standards.

Across 5,469 monitored lakes in 12 states, 26% earn an A grade for water quality and 50% earn an A or B. The top 50 cleanest below draw from 1 state, led by Minnesota with 50 — 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 East Fox Lake in Crow Wing County, MN — Grade A, with 16.4 feet of water clarity and phosphorus of 10 µg/L. Below that, the rest of the top 10 fall in a tight clarity band, with the gap between #1 and #10 typically less than three feet of Secchi depth.

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 3 Cleanest Lakes

#1A

East Fox Lake

Crow Wing County, MN

The cleanest lake on our 12-state index. Water clarity 16.4 feet, phosphorus 10 µg/L. Max depth 65 ft.

#2A

North Long Lake

Crow Wing County, MN

Second-cleanest with Grade A. Secchi depth 15.1 ft. Max depth 97 ft.

#3A

Bad Medicine Lake

Becker County, MN

Third-cleanest, Grade A. Max depth 84 ft.

Rank	Lake	County	State	Grade	Clarity	Max Depth
1	East Fox Lake	Crow Wing	MN	A	16.4 ft	65 ft
2	North Long Lake	Crow Wing	MN	A	15.1 ft	97 ft
3	Bad Medicine Lake	Becker	MN	A	25 ft	84 ft
4	Big Sugar Bush Lake	Becker	MN	A	16.5 ft	42 ft
5	Round Lake	Cook	MN	A	16.5 ft	45 ft
6	Round Lake	Beltrami	MN	A	18 ft	38 ft
7	Horseshoe Lake	Cass	MN	A	21 ft	51 ft
8	Long Lake	Cass	MN	A	21.5 ft	115 ft
9	Long Lake	Clearwater	MN	A	20.5 ft	80 ft
10	Long Lake	Beltrami	MN	A	20 ft	87 ft
11	Long Lake	Becker	MN	A	19.3 ft	61 ft
12	Long Lake	Itasca	MN	A	16.7 ft	72 ft
13	Dead Lake	Hubbard	MN	A	16 ft	34 ft
14	West Twin Lake	Crow Wing	MN	A	20 ft	-
15	Sunshine Lake	St. Louis	MN	A	20 ft	37 ft
16	Otter Lake	Otter Tail	MN	A	18 ft	64 ft
17	Ossawinnamakee Lake	Crow Wing	MN	A	20 ft	63 ft
18	Clear Lake	Crow Wing	MN	A	18 ft	63 ft
19	Clear Lake	Aitkin	MN	A	15 ft	24 ft
20	Clear Lake	Itasca	MN	A	14.9 ft	30 ft
21	Eagle Lake	Otter Tail	MN	A	22.6 ft	46 ft
22	West Fox Lake	Crow Wing	MN	A	15 ft	55 ft
23	Spearhead Lake	Hubbard	MN	A	15 ft	81 ft
24	Ida Lake	Douglas	MN	A	16.4 ft	106 ft
25	Star Lake	Crow Wing	MN	A	19 ft	83 ft
26	Star Lake	Otter Tail	MN	A	17 ft	94 ft
27	Upper Maple Lake	Wright	MN	A	17.2 ft	76 ft
28	Fish Lake	Otter Tail	MN	A	18 ft	69 ft
29	Jenny Lake	Lake	MN	A	15.5 ft	93 ft
30	Hamlet Lake	Crow Wing	MN	A	18.5 ft	88 ft
31	Birch Lake	Wright	MN	A	15 ft	52 ft
32	Birch Lake	Cook	MN	A	18 ft	69 ft
33	Birch Lake	Unknown	MN	A	15 ft	34 ft
34	Woman Lake	Cass	MN	A	15 ft	-
35	Girl Lake	Cass	MN	A	17.6 ft	81 ft
36	Little Toad Lake	Becker	MN	A	15 ft	65 ft
37	Charlotte Lake	Wright	MN	A	17.1 ft	46 ft
38	Bass Lake	Otter Tail	MN	A	17.4 ft	-
39	Bass Lake	Crow Wing	MN	A	16.1 ft	47 ft
40	Bass Lake	Itasca	MN	A	18.2 ft	65 ft
41	Bass Lake	Cass	MN	A	-	55 ft
42	Crooked Lake	Stearns	MN	A	15.5 ft	35 ft
43	Crooked Lake	Hubbard	MN	A	19 ft	-
44	Crooked Lake	Crow Wing	MN	A	15 ft	54 ft
45	Cedar Lake	Morrison	MN	A	16.2 ft	88 ft
46	Pelican Lake	Otter Tail	MN	A	16.4 ft	55 ft
47	Square Lake	Washington	MN	A	17 ft	68 ft
48	Lower Bottle Lake	Hubbard	MN	A	15 ft	110 ft
49	Big Pine Lake	Aitkin	MN	A	17 ft	78 ft
50	Strawberry Lake	Becker	MN	A	17.5 ft	40 ft

Frequently Asked Questions

East Fox Lake in Crow Wing County, MN, is the highest-rated lake on our index with a Grade A for overall water quality. Its water clarity (Secchi depth) reads 16.4 feet, with phosphorus at 10 µg/L.

Lakes earn a letter grade A-F based on three metrics from state and EPA monitoring programs: water clarity (Secchi depth in feet — deeper is better), total phosphorus (µg/L — lower is better, since phosphorus drives algae blooms), and chlorophyll-a (µg/L — measures algae directly). Grades use Metropolitan Council water-quality standards.

Of 5,469 lakes across our 12-state database, 1,395 (26%) earn an A grade for overall water quality. Another 1,338 earn a B, bringing the total of A-or-B lakes to 2,733 (50%).

Mostly yes, but not always. Water clarity correlates strongly with low algae and low phosphorus — the same factors that drive harmful algal blooms (HABs). But clarity alone does not measure E. coli, bacterial contamination, or chemical pollutants from runoff. Always check your state agency for current swimming advisories on a specific beach before swimming.

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.

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