Question 1

What are the cleanest lakes in the US?

Accepted Answer

There is no single official national ranking — water quality is graded state-by-state by different agencies using different metrics. LakeQuality fixes that by grading lakes across 38 states (MN, WI, IL, MI, IA, OH, PA, NY, MO, IN, ND, SD, FL, CO, NC, VT, TX, OR, AR, OK, KS, NE, NV, AZ, ID, MT, NM, TN, AL, VA, KY, UT, WA, WY, GA, MA, ON, QC) on one uniform A–F scale, using Secchi depth (clarity), total phosphorus, and chlorophyll-a — the three signals scientists use to measure lake health. The lakes ranked here have the highest combined scores in our 2026 dataset, so they are the cleanest lakes in the US among every waterbody we monitor.

Question 2

How do you rank the cleanest lakes?

Accepted Answer

We score every monitored lake on three water-quality signals: Secchi depth (water clarity, deeper is better), total phosphorus (lower is better — phosphorus drives algae growth), and chlorophyll-a (lower is better — measures algae density). Each signal gets a 0–100 sub-score; the three are averaged into an overall score that maps to an A–F grade. Lakes here are ranked by their overall score.

Question 3

Is a clean lake safe to swim in?

Accepted Answer

Generally yes — lakes with grade A or B and chlorophyll-a below 10 µg/L are unlikely to host harmful algal blooms during normal conditions. But water quality changes seasonally. Always check for posted advisories before swimming, especially in late summer when blue-green algae blooms peak.

Question 4

What is Secchi depth?

Accepted Answer

Secchi depth is a clarity measurement. A black-and-white disk is lowered into the water; the depth at which it disappears (in feet or meters) is the Secchi depth. Greater depth means clearer water. Across our dataset, A-grade lakes typically have Secchi depths above 10 feet.

Question 5

Why is Minnesota called the Land of 10,000 Lakes?

Accepted Answer

Minnesota actually has about 11,842 lakes ≥10 acres — far more than the marketing slogan suggests. Wisconsin has roughly 15,000 named lakes by some counts (including very small ones). Combined, the two states cover more freshwater lakes than nearly any equivalent area in North America. LakeQuality now grades lakes across 38 states, so you can compare the cleanest water beyond the two lake-country classics.

Rank	Lake	County	State	Grade	Clarity	Phosphorus	Area
1	Rainy Lake	Cass	MN	A	13.9 ft	11.5 µg/L	129 acres
2	Crane Lake	Otter Tail	MN	A	9 ft	15 µg/L	350 acres
3	Lobster Lake	Douglas	MN	A	13 ft	20.5 µg/L	1,334 acres
4	East Fox Lake	Crow Wing	MN	A	16.4 ft	10 µg/L	241 acres
5	Deep Portage Lake	Cass	MN	A	15.4 ft	9 µg/L	129 acres
6	Clearwater Lake	Cook	MN	A	29 ft	4 µg/L	462 acres
7	Clearwater Lake	Wright	MN	A	9.8 ft	22 µg/L	3,187 acres
8	Clearwater Lake	Clearwater	MN	A	10 ft	16 µg/L	999 acres
9	Lower Hay Lake	Crow Wing	MN	A	18.5 ft	13 µg/L	700 acres
10	Latoka Lake	Douglas	MN	A	19 ft	11 µg/L	767 acres
11	Big Cedar Lake-North Site-Near West Bend	Washington	WI	A	11.8 ft	17.5 µg/L	937 acres
12	Big Cedar Lake-South Site-Near West Bend	Washington	WI	A	12.6 ft	14.5 µg/L	937 acres
13	Green Lake	Green Lake	WI	A	13.5 ft	38.1 µg/L	7,920 acres
14	Lake Beulah	Walworth	WI	A	10 ft	13.4 µg/L	812 acres
15	Okauchee Lake	Waukesha	WI	A	11.5 ft	18 µg/L	1,210 acres
16	Geneva Lake	Walworth	WI	A	21 ft	13 µg/L	5,401 acres
17	Powers Lake	Kenosha	WI	A	10 ft	17.2 µg/L	451 acres
18	Lac Courte Oreilles Lake	Sawyer	WI	A	12.2 ft	15 µg/L	5,139 acres
19	Whitefish Lake	Sawyer	WI	A	13.5 ft	14 µg/L	800 acres
20	Round Lake	Sawyer	WI	A	21.1 ft	14 µg/L	3,294 acres
21	Lake Calumet	Cook	IL	A	4.1 ft	16.5 µg/L	0 acres
22	Chippewa Lake Northeast Basin; Chippewa Township	Mecosta	MI	A	12.8 ft	18 µg/L	-
23	Windover Lake South Basin; Freeman Township	Clare	MI	A	15 ft	9 µg/L	-
24	Moon Lake Central Basin; Watersmeet Township	Gogebic	MI	A	18 ft	7 µg/L	-
25	West Twin Lake East Basin; Albert Township	Montmorency	MI	A	13 ft	9 µg/L	-
26	Eagle Lake West Central Basin; Ontwa Township	Cass	MI	A	6.3 ft	12 µg/L	-
27	East Twin Lake South Central Basin; Albert Township	Montmorency	MI	A	10 ft	14 µg/L	-
28	Brooks Lake	Leelanau	MI	A	9 ft	10 µg/L	-
29	Indian Lake Central Basin; Brady Township	Kalamazoo	MI	A	9.5 ft	12 µg/L	-
30	Sunset Lake West Central Basin; Bates Township	Iron	MI	A	15.5 ft	7 µg/L	-
31	Big Bass Lake North Basin; Elk Township	Lake	MI	A	14 ft	8 µg/L	-
32	West Okoboji Lake	Dickinson	IA	A	15.7 ft	20 µg/L	-
33	Dale Maffitt Reservoir	Dallas	IA	A	9.8 ft	20 µg/L	230 acres
34	Blue Pit Lake	Cerro Gordo	IA	A	17.1 ft	20 µg/L	-
35	Ada Hayden Heritage Park Lake	Story	IA	A	6.8 ft	19 µg/L	-
36	Nine Eagles Lake	Decatur	IA	A	11 ft	15.5 µg/L	59 acres
37	Little Sioux Park Lake	Woodbury	IA	A	5.7 ft	19 µg/L	-
38	Rudd Lake	Floyd	IA	A	8.1 ft	14 µg/L	-
39	Slipbluff Lake	Decatur	IA	A	9 ft	17.5 µg/L	18 acres
40	Lacey Keosauqua Lake	Van Buren	IA	A	7.1 ft	21.5 µg/L	23 acres
41	Yenruogis Pond	Keokuk	IA	A	9.9 ft	21 µg/L	-
42	Queneska Island Lake	Essex	NY	A	17.4 ft	15 µg/L	-
43	South Lake	Herkimer	NY	A	—	4 µg/L	499 acres
44	West Pond	Herkimer	NY	A	—	10 µg/L	-
45	Squash Pond	Herkimer	NY	A	—	11 µg/L	-
46	Sherwood Lake	Warren	MO	A	5.9 ft	14.3 µg/L	145 acres
47	Lake Taneycomo @ Rockaway Beach	Taney	MO	A	8.7 ft	13.5 µg/L	-
48	Fox Valley Lake	Clark	MO	A	8.5 ft	16.5 µg/L	96 acres
49	Table Rock Lk. Into Main Channel From Dam Lake	Stone	MO	A	7.2 ft	8 µg/L	43,100 acres
50	Clearwater Lake	Wayne	MO	A	5.7 ft	15.7 µg/L	-

Cleanest Lakes in the US

Frequently Asked Questions