What is the cleanest lake in Wisconsin?

Big Cedar Lake-North Site-Near West Bend in Washington County is the highest-rated lake in Wisconsin with an EPA water quality grade of A and 11.8 feet of water clarity.

How are these rankings calculated?

Lakes are graded A through F on nutrients and algae — total phosphorus, nitrogen, chlorophyll-a, and turbidity — against EPA National Lakes Assessment 2022 condition classes for that lake’s ecoregion. Water clarity (Secchi depth) is measured and shown; it is not the letter. Lakes without enough recent samples are UNRATED, not given an F. Source data comes from the EPA Water Quality Portal.

Safest Lakes to Swim In in Wisconsin

33 lakes in Wisconsin qualify as safest for swimming, all hold grade A or B and report chlorophyll-a (algae) under 10 µg/L. Always check local advisories on the day you swim.

Ranked List

#	Lake	County	Grade	Clarity	Phosphorus	Algae
1	Big Cedar Lake-North Site-Near West Bend	Washington	A	11.8 ft	17.5 µg/L	3.6 µg/L
2	Green Lake	Green Lake	A	13.5 ft	38.1 µg/L	4.4 µg/L
3	Lake Beulah	Walworth	A	10 ft	13.4 µg/L	2.5 µg/L
4	Geneva Lake	Walworth	A	21 ft	13 µg/L	2.1 µg/L
5	Powers Lake	Kenosha	A	10 ft	17.2 µg/L	3.4 µg/L
6	Lac Courte Oreilles Lake	Sawyer	A	12.2 ft	15 µg/L	1.7 µg/L
7	Whitefish Lake	Sawyer	A	13.5 ft	14 µg/L	1.6 µg/L
8	Round Lake	Sawyer	A	21.1 ft	14 µg/L	0.9 µg/L
9	Indian Lake	Sawyer	A	6.5 ft	22.5 µg/L	3.6 µg/L
10	Big Lake	Shawano	A	8 ft	15 µg/L	2.7 µg/L
11	Christner Lake	Sawyer	A	12 ft	18.5 µg/L	2.1 µg/L
12	Sand Lake	Barron	A	13 ft	20 µg/L	1.9 µg/L
13	Sand Lake	Sawyer	A	10 ft	23.8 µg/L	4.1 µg/L
14	Ashegon Lake	Sawyer	A	10.5 ft	18 µg/L	2.7 µg/L
15	Blueberry Lake	Sawyer	A	14.8 ft	17 µg/L	1.6 µg/L
16	Koonz Lake	Shawano	A	10.8 ft	17 µg/L	1.7 µg/L
17	Little Round Lake	Sawyer	A	17.3 ft	12 µg/L	1 µg/L
18	Osprey Lake	Sawyer	A	16 ft	14.9 µg/L	1.4 µg/L
19	Grindstone Lake	Sawyer	A	17.4 ft	15 µg/L	1.4 µg/L
20	Lost Lake	Sawyer	A	10.6 ft	19.5 µg/L	1.6 µg/L
21	Gaslyn Lake	Burnett	A	4.5 ft	31.5 µg/L	4.2 µg/L
22	Durphee Lake	Sawyer	A	8.1 ft	22 µg/L	3.1 µg/L
23	Malone Lake	Shawano	A	13.5 ft	18 µg/L	2.1 µg/L
24	Sams Lake	Shawano	A	11 ft	18 µg/L	2.2 µg/L
25	Oneida Lake	Outagamie	A	-	15 µg/L	1.4 µg/L
26	Mission Lake	Shawano	A	17.5 ft	17 µg/L	2.1 µg/L
27	Bealeau Lake	Shawano	A	11.5 ft	17 µg/L	2.2 µg/L
28	King Lake	Marinette	A	-	9 µg/L	0.8 µg/L
29	Mole Lake	Forest	A	8.5 ft	15.6 µg/L	1.3 µg/L
30	Bug Lake	Forest	A	-	9.5 µg/L	1 µg/L
31	Cloud Lake	Forest	A	-	13 µg/L	1.2 µg/L
32	Devil'S Lake	Forest	A	-	22 µg/L	2.5 µg/L
33	Quarry Lake	Brown	B	8 ft	34 µg/L	9.6 µg/L

Ranked List

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