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LakeQuality

Cleanest Lakes in Wisconsin

Windover Lake South Basin; Freeman Township ranks #1 for water quality in Wisconsin with a grade of A. Below: the top 25 cleanest lakes in Wisconsin by combined Secchi clarity, phosphorus, and chlorophyll-a from 2026 EPA + DNR sampling.

Filtered to remove lakes with limited data (<3 sampling years). Sorted by overall water quality score.

The "cleanest" ranking on LakeGrade is composite: water clarity (Secchi), total phosphorus, and chlorophyll-a — the three core inputs to the LakeGrade rubric — taken together. The cleanest Michigan lake on the current data is Windover Lake South Basin; Freeman Township (A).

The top of the cleanest-lakes list is dominated by deep, glacial, cold-water basins — the same basins that produce the A-grade bracket overall. The pattern is not coincidence: depth and watershed land-use are the dominant inputs to water-clarity and nutrient-loading both.

RankLakeCountyGradeClarityPhosphorusChlorophyll-aArea
1Windover Lake South Basin; Freeman TownshipClareA15 ft—2.5 µg/L-
2Moon Lake Central Basin; Watersmeet TownshipGogebicA18 ft—3.2 µg/L-
3East Arm Grand Traverse Bay 2 Mi From South Shore LakeGrand TraverseA36.6 ft—1.2 µg/L-
4Sunset Lake West Central Basin; Bates TownshipIronA15.5 ft—2.2 µg/L-
5West Arm Grand Traverse Bay 3 Mi Southeast Stony Point LakeGrand TraverseA41.4 ft—1.1 µg/L-
6Glen Lake North Cent Basin; Glen Arbor Township Section 35LeelanauA22 ft—1.3 µg/L-
7Ellen Lake South Central Basin; Mansfield TownshipIronA17 ft—2.8 µg/L-
8Smoky LakeIronA24 ft8.3 µg/L—-
9East Arm Grand Traverse Bay 2.5 Mi From North End LakeGrand TraverseA37.3 ft—1.1 µg/L-
10West Arm Grand Traverse Bay 2 Mi From South Shore LakeLeelanauA38.2 ft—1 µg/L-
11Whitefish Bay Deep LakeChippewaA34.4 ft16 µg/L2.5 µg/L-
12Little Bass LakeLakeA18.3 ft—3.1 µg/L-
13Whitefish Lake Southeast Basin; Pierson TownshipMontcalmA16 ft—3.4 µg/L-
14Crystal Lake Central Basin; Lake Township Section 12BenzieA32 ft—1.1 µg/L-
15Avery Lake North Basin; T29nr2eMontmorencyA27 ft—1.5 µg/L-
16Cobb Lake Central BasinBarryA16 ft—1.8 µg/L-
17Lake Mary Northwest Basin; Mastodon TownshipIronA18 ft—3 µg/L-
18Big Twin Lake Southeast Basin; Blue Lake TownshipKalkaskaA23 ft—2.3 µg/L-
19Round LakeBenzieA15 ft—2.7 µg/L-
20Bills Lake Central BasinNewaygoA15.5 ft—1.7 µg/L-
21Bear Lake Southeast BasinKalkaskaA36.5 ft—2.4 µg/L-
22Arbutus Lake South Central BasinGrand TraverseA19 ft—2.1 µg/L-
23Cub Lake Central BasinKalkaskaA19 ft—1.7 µg/L-
24Island Lake East Basin; Whitewater Township Section 31Grand TraverseA16 ft—2 µg/L-
25Arnold Lake North Central Basin; Hayes Township Sec. 2ClareA18 ft—1.2 µg/L-
Combined MN + WI list →Minnesota version →Best swimming lakes in Wisconsin →All Wisconsin lakes →Most polluted lakes →

Frequently Asked Questions

What is the cleanest lake in Wisconsin?

Windover Lake South Basin; Freeman Township has the highest water quality score in our 2026 Wisconsin dataset (grade A), based on combined Secchi clarity, phosphorus, and chlorophyll-a measurements. Cleanliness here means low nutrient load, deep water clarity, and minimal algae — measured directly from EPA and state DNR samples.

What is the most polluted lake in Wisconsin?

Among monitored Wisconsin lakes, Palmer Lake Central Basin; Colon Township ranks among the most polluted by combined phosphorus and chlorophyll-a load. See our full ranking on the most-polluted-lakes trend page for state-by-state details.

Where in Wisconsin has the cleanest water?

Wisconsin's clearest waters are concentrated in the deeper, lower-nutrient lakes of the state's northeast — typically older glacial lakes with rocky basins and forested watersheds. The top 25 above shows the highest-scoring lakes statewide; counties like Cook, Lake, and Itasca (MN) or Vilas, Oneida, and Iron (WI) consistently produce A-grade waters.

Are these lakes safe to swim in?

A and B grade lakes are typically safe for swimming under normal conditions. Chlorophyll-a below 10 µg/L means low risk of harmful algal blooms. Always check posted advisories before swimming — water quality changes seasonally, especially in late summer when blue-green algae bloom risk peaks.

How are these grades calculated?

Each lake is scored on three signals: Secchi depth (water clarity in feet), total phosphorus (nutrient load in µg/L), and chlorophyll-a (algae concentration in µg/L). Each gets a 0–100 sub-score relative to Wisconsin state norms. The three sub-scores average into the overall score, which maps to an A–F letter grade. Methodology details live on our methodology page.

What are the top 5 cleanest lakes in the US?

There is no single national ranking of cleanest lakes — each state agency uses different metrics. Crater Lake (Oregon) is widely cited as the clearest US lake, with Secchi depths over 30 m. Lake Tahoe and Lake Superior are also top-tier nationally. Within Wisconsin, the lakes ranked above are the top 25 by our standardized 2026 grading.

How we rank cleanest lakes

Cleanliness here means three things working together:

  • Secchi clarity — how deep you can see into the water (in feet). Greater depth = clearer water = lower suspended sediment and algae.
  • Total phosphorus — the nutrient that fuels algae. Lower phosphorus levels mean less algae growth potential.
  • Chlorophyll-a — the green pigment in algae. Direct measurement of how much algae is currently in the water.

Each signal is normalized against Wisconsin state norms and combined into a single 0–100 score. The lakes above are sorted by that combined score.Full methodology →

Source: EPA National Aquatic Resource Surveys, 2026.