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.

Cleanest Lakes in Wisconsin

Big Cedar Lake-North Site-Near West Bend in Washington County leads the rankings with a water quality grade of A and 11.8 ft of clarity. Below are the top 50 cleanest monitored lakes in Wisconsin, ranked by EPA water quality score.

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	Wind Lake	Polk	B	10 ft	17.2 µg/L	-
34	Green Lake	Walworth	B	11 ft	10.7 µg/L	-
35	Green Lake	Washington	B	9 ft	16.6 µg/L	-
36	Boulder Lake	Oconto	B	11 ft	13.3 µg/L	-
37	Spider Lake	Iron	B	8.5 ft	14.4 µg/L	-
38	Spider Lake	Sawyer	B	10.5 ft	14.1 µg/L	-
39	Spider Lake	Vilas	B	10.5 ft	14.1 µg/L	-
40	Pickerel Lake	Forest	B	10 ft	20.4 µg/L	-
41	Pickerel Lake	Oconto	B	8 ft	15.6 µg/L	-
42	Pickerel Lake	Vilas	B	6 ft	23 µg/L	-
43	Pickerel Lake	Lincoln	B	-	20.3 µg/L	-
44	Carpenter Lake	Vilas	B	7.5 ft	17 µg/L	-
45	Cranberry Lake	Burnett	B	8.8 ft	14.1 µg/L	-
46	Beaver Dam Lake	Barron	B	11 ft	12.9 µg/L	-
47	North Turtle Lake	Vilas	B	8.5 ft	15.4 µg/L	-
48	Balsam Lake	Washburn	B	8.8 ft	19.3 µg/L	-
49	Silver Lake	Kenosha	B	7.1 ft	18.2 µg/L	-
50	Silver Lake	Waukesha	B	10 ft	11.8 µg/L	-

Ranked List

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