Updated August 2026

Cleanest Lakes in the US

The 50 cleanest lakes in the US, ranked by 2026 water quality data. LakeQuality grades 5,737 lakes. Ontario and Québec have 0 letters and are not in this grade ranking. Other country hubs are not on the A–F scale. The letter is nutrients and algae. Secchi is not scored. Among lakes that share a letter, a deeper Secchi and lower phosphorus break the tie.

Looking for the famous border lake? This #1 is the 129-acre Rainy Lake in Cass County. The much larger Rainy Lake on the Minnesota–Ontario border is a different lake — open Rainy Lake (Koochiching County, MN).

All 50 with clarity, phosphorus and surface area

Rank	Lake	County	State	Grade	Clarity	Phosphorus	Area
1	Rainy Lake (Cass County, MN)	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	Green Lake	Green Lake	WI	A	13.5 ft	38.1 µg/L	7,920 acres
12	Lake Beulah	Walworth	WI	A	10 ft	13.4 µg/L	812 acres
13	Geneva Lake	Walworth	WI	A	21 ft	13 µg/L	5,401 acres
14	Powers Lake	Kenosha	WI	A	10 ft	17.2 µg/L	451 acres
15	Lac Courte Oreilles Lake	Sawyer	WI	A	12.2 ft	15 µg/L	5,139 acres
16	Whitefish Lake	Sawyer	WI	A	13.5 ft	14 µg/L	800 acres
17	Round Lake	Sawyer	WI	A	21.1 ft	14 µg/L	3,294 acres
18	Indian Lake	Sawyer	WI	A	6.5 ft	22.5 µg/L	76 acres
19	Big Lake	Shawano	WI	A	8 ft	15 µg/L	-
20	Christner Lake	Sawyer	WI	A	12 ft	18.5 µg/L	36 acres
21	Lake Calumet	Cook	IL	A	4.1 ft	16.5 µg/L	0 acres
22	Crystal Lake	Montcalm	MI	A	10 ft	9 µg/L	709 acres
23	Ore Lake	Livingston	MI	A	9 ft	22 µg/L	229 acres
24	South Bar Lake	Leelanau	MI	A	8.5 ft	14 µg/L	78 acres
25	Eagle Lake	Kalkaska	MI	A	18 ft	10 µg/L	25 acres
26	Ellen Lake	Iron	MI	A	17.3 ft	8 µg/L	140 acres
27	Brooks Lake	Leelanau	MI	A	9.5 ft	10 µg/L	7 acres
28	Indian Lake	Kalamazoo	MI	A	9.5 ft	10 µg/L	790 acres
29	Round Lake	Mecosta	MI	A	9 ft	17 µg/L	157 acres
30	Mecosta Lake	Mecosta	MI	A	9.5 ft	10 µg/L	312 acres
31	Perch Lake	Iron	MI	A	6 ft	24 µg/L	1,046 acres
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	Little Sioux Park Lake	Woodbury	IA	A	5.7 ft	19 µg/L	-
37	Rudd Lake	Floyd	IA	A	8.1 ft	14 µg/L	-
38	Slipbluff Lake	Decatur	IA	A	9 ft	17.5 µg/L	18 acres
39	Lacey Keosauqua Lake	Van Buren	IA	A	7.1 ft	21.5 µg/L	23 acres
40	Yenruogis Pond	Keokuk	IA	A	9.9 ft	21 µg/L	-
41	Sand Lake	Marshall	IA	A	6.4 ft	25 µg/L	-
42	Belmont Lake	Wayne	PA	A	—	14.5 µg/L	173 acres
43	Mountain Mud Pond	Lackawanna	PA	A	—	13.5 µg/L	30 acres
44	Lake Marburg	York	PA	A	—	14 µg/L	1,173 acres
45	Long Pine Run Reservoir	Adams	PA	A	—	6.5 µg/L	151 acres
46	Queneska Island Lake	Essex	NY	A	17.4 ft	15 µg/L	-
47	South Lake	Herkimer	NY	A	—	4 µg/L	499 acres
48	West Pond	Herkimer	NY	A	—	10 µg/L	-
49	Squash Pond	Herkimer	NY	A	—	11 µg/L	-
50	Sherwood Lake	Warren	MO	A	5.9 ft	14.3 µg/L	145 acres

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Frequently Asked Questions

What are the cleanest lakes in the US?

There is no single official national ranking — water quality is graded state-by-state by different agencies using different metrics. LakeQuality grades 5,737 lakes. Ontario and Québec have 0 letters and are not in this grade ranking. Other country hubs are not on the A–F scale. Nutrients and algae against EPA National Lakes Assessment 2022 ecoregion classes. The lakes ranked here have the highest letters in our 2026 dataset, so they are the cleanest lakes in the US among every waterbody we monitor.

What is the cleanest lake in the US?

There is no official national "cleanest lake" designation. On this ranking the #1 lake is the highest 2026 letter. LakeQuality grades 5,737 lakes. Ontario and Québec have 0 letters and are not in this grade ranking. Other country hubs are not on the A–F scale. The letter is not a swimming clearance — check local advisories before you get in.

How do you rank the cleanest lakes?

The letter is nutrients and algae — phosphorus, nitrogen, chlorophyll-a, and turbidity — scored against EPA National Lakes Assessment 2022 cutpoints for that lake’s ecoregion. Water clarity (Secchi depth) is measured and shown; it is not scored. Among lakes that share a letter, a deeper Secchi and lower phosphorus break the tie. Lakes without enough recent sampling are UNRATED and are not on this list. Our methodology page has the full rubric.

Is a clean lake safe to swim in?

Not on the letter alone. An A or B is a nutrients-and-algae classification, not a swimming clearance — it does not measure E. coli, cyanotoxins, or a posted beach closure. Always check current local advisories before swimming, especially in late summer when blue-green algae blooms peak.

What is Secchi depth?

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.

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

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 grades 5,737 lakes. Ontario and Québec have 0 letters and are not in this grade ranking. Other country hubs are not on the A–F scale.

More on clean water

Cleanest and Dirtiest Lakes in America 2026

The cleanest and dirtiest U.S. lakes in the monitoring record, ranked on EPA nutrient and algae condition classes across thousands of graded lakes.

Lake Water Quality Grades Explained: What A–F Means

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.

Cleanest Small Lakes in America 2026

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.

How to Choose a Clean Lake for a Cabin or Weekend Trip

A practical checklist for picking a lake with good water quality — clarity, phosphorus, algae history, depth, and the data to check before you commit.