Updated Aug 2026
Wisconsin Lake Water Quality
Water quality grades for 1,428 monitored lakes across 69 counties.
Wisconsin has 1,428 graded lakes in our dataset, sampled across 69 counties. The Wisconsin DNR runs a Citizen Lake Monitoring Network that contributes a large share of the actual measurements. A-grade lakes are scarce in Wisconsin: about 3% of the dataset. Most lakes here sit in C or D — productive, often shallow, frequently algal in late summer.
Mesotrophic is the dominant trophic class — a workable middle ground between the pristine oligotrophic deep lakes and the algal-pressured eutrophic shallow ones. The cleanest county on average is Outagamie (grade A); the most-stressed is Dunn. The gap between the top and bottom counties is large enough that "Wisconsin lake water quality" hides real local variation.
Grade Distribution
All 1,428 Wisconsin lakes in the index: 853 (59.7%) carry an A–F grade and 575 (40.3%) are not rated — their monitoring record does not meet the evidence bar.
Where to stay near Wisconsin
Top-rated places to stay near Wisconsin
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Top-Graded Wisconsin Lakes
The highest water-quality grades in Wisconsin — clarity, depth, and A-F grade at a glance.
Lake Map
Explore Wisconsin Lakes
Wisconsin reports, fishing & travel
Wisconsin's cleanest and most-polluted lakes, ranked A–F
Fish species and top-graded lakes across Wisconsin
Species activity outlook by water temperature and season
Where to stay at Wisconsin's top lakes, each with its grade
Best-graded lakes within 50 miles of Milwaukee
Best-graded lakes within 50 miles of Madison
Best-graded lakes within 50 miles of Green Bay
Best-graded lakes within 50 miles of Eau Claire
Best-graded lakes within 50 miles of Wausau
Best-graded lakes within 50 miles of La Crosse
Reservoirs in Wisconsin
View all 197 reservoirs →197 of 1,428 Wisconsin lakes (14%) are man-made reservoirs in the USACE National Inventory of Dams. 87 carry a High or Significant hazard rating. The oldest matched dam dates to 1836.
EPA-Impaired Lakes in Wisconsin
View all 509 impaired lakes →509 of 1,428 Wisconsin lakes (36%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 75 have an approved Total Maximum Daily Load (TMDL) restoration plan.
Wisconsin Fishing & Recreation
Licenses, regulations, records, and where to fish across Wisconsin.
Counties
All 69 Wisconsin counties, ranked by average lake water quality. Compare them against every county nationwide in the county rankings, browse the full directory of graded lakes, or pick a different state.
Wisconsin Lake Water Quality Dataset (2026)
Every graded Wisconsin lake in one spreadsheet — A–F grade, water clarity, phosphorus, chlorophyll-a, trophic state, size, public access, and a link to each lake's report card.
Top 25 Cleanest Lakes
25 lakes25 graded lakes
| # | Lake | County | Grade | Clarity | Trophic | Max Depth | Access |
|---|---|---|---|---|---|---|---|
| 1 | ABig Cedar Lake-North Site-Near West Bend | Washington | A | 11.8 ft | Mesotrophic | 105 ft | ✓ Public |
| 2 | ABig Cedar Lake-South Site-Near West Bend | Washington | A | 12.6 ft | Mesotrophic | 105 ft | ✓ Public |
| 3 | AGreen Lake | Green Lake | A | 13.5 ft | Mesotrophic | 236 ft | ✓ Public |
| 4 | ALake Beulah | Walworth | A | 10 ft | Mesotrophic | 58 ft | ✓ Public |
| 5 | AOkauchee Lake | Waukesha | A | 11.5 ft | Mesotrophic | 90 ft | ✓ Public |
| 6 | AGeneva Lake | Walworth | A | 21 ft | Oligotrophic | 135 ft | ✓ Public |
| 7 | APowers Lake | Kenosha | A | 10 ft | Mesotrophic | 33 ft | ✓ Public |
| 8 | ALac Courte Oreilles Lake | Sawyer | A | 12.2 ft | Mesotrophic | 90 ft | ✓ Public |
| 9 | AWhitefish Lake | Sawyer | A | 13.5 ft | Oligotrophic | 105 ft | ✓ Public |
| 10 | ARound Lake | Sawyer | A | 21.1 ft | Oligotrophic | 74 ft | ✓ Public |
| 11 | AIndian Lake | Sawyer | A | 6.5 ft | Mesotrophic | 9 ft | ✓ Public |
| 12 | ABig Sand Lake | Burnett | A | 11 ft | Mesotrophic | 55 ft | ✓ Public |
| 13 | ABig Lake | Shawano | A | 8 ft | Mesotrophic | No recent samples | Not recorded |
| 14 | ALittle Lac Courte Oreilles Lake | Sawyer | A | 12 ft | Mesotrophic | 46 ft | Not recorded |
| 15 | AChristner Lake | Sawyer | A | 12 ft | Mesotrophic | 16 ft | Not recorded |
| 16 | ASand Lake | Barron | A | 13 ft | Mesotrophic | No recent samples | ✓ Public |
| 17 | ASand Lake | Sawyer | A | 10 ft | Mesotrophic | 50 ft | ✓ Public |
| 18 | AAshegon Lake | Sawyer | A | 10.5 ft | Mesotrophic | 56 ft | ✓ Public |
| 19 | ABlueberry Lake | Sawyer | A | 14.8 ft | Oligotrophic | 29 ft | ✓ Public |
| 20 | AKoonz Lake | Shawano | A | 10.8 ft | Mesotrophic | 40 ft | ✓ Public |
| 21 | ALittle Round Lake | Sawyer | A | 17.3 ft | Oligotrophic | 38 ft | Not recorded |
| 22 | AOsprey Lake | Sawyer | A | 16 ft | Oligotrophic | 32 ft | ✓ Public |
| 23 | AGrindstone Lake | Sawyer | A | 17.4 ft | Oligotrophic | 60 ft | ✓ Public |
| 24 | ALost Lake | Sawyer | A | 10.6 ft | Mesotrophic | 13 ft | Not recorded |
| 25 | AGaslyn Lake | Burnett | A | 4.5 ft | Eutrophic | 12 ft | ✓ Public |
25 Lakes Needing Attention
25 lakes25 graded lakes
| # | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | DGiltners Lake | Fond du Lac | D | No recent samples |
| 2 | DWyona Lake | Columbia | D | No recent samples |
| 3 | DSilver Creek Estuary Lake | Green Lake | D | No recent samples |
| 4 | DCounty K Marsh Lake | Green Lake | D | No recent samples |
| 5 | DCulvert on Lake Helen | Portage | D | No recent samples |
| 6 | DLake Tomah | Monroe | D | No recent samples |
| 7 | DTilleda Pond | Shawano | D | No recent samples |
| 8 | DDecorah Lake | Juneau | D | No recent samples |
| 9 | DLanding Lake | Wood | D | No recent samples |
| 10 | DCathedral Point Pond | Dane | D | No recent samples |
| 11 | DPrairie Oaks Pond | Dane | D | No recent samples |
| 12 | DLake Chetac | Sawyer | D | No recent samples |
| 13 | DDewitt Road-Cedar Grove Lake | Sheboygan | D | No recent samples |
| 14 | DOutlet To Lake Geneva | Walworth | D | No recent samples |
| 15 | DSilent Street Pond | Dane | D | No recent samples |
| 16 | DAmerican Way Pond | Dane | D | No recent samples |
| 17 | DMuskego Lake | Waukesha | D | No recent samples |
| 18 | DWhalen Road Pond | Dane | D | No recent samples |
| 19 | DBirch Lake | Sawyer | D | No recent samples |
| 20 | DLake Chetac North Basin | Sawyer | D | No recent samples |
| 21 | DInvestment Court Pond | Dane | D | No recent samples |
| 22 | DDexter Lake | Wood | D | 1.5 ft |
| 23 | DRadigan Flowage Lake | Douglas | D | 2 ft |
| 24 | DBig Blake Lake | Polk | D | 2.5 ft |
| 25 | DHill Slough Lake | Sauk | D | 4.4 ft |
Lake Match
Which lake suits how you actually use one?
Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of graded lakes that fit, with the water quality behind each one.
Source: EPA National Aquatic Resource Surveys and the EPA Water Quality Portal.