Wisconsin Lake Water Quality
Water quality grades for 16 monitored lakes across 13 counties.
A-grade lakes are scarce in South Dakota: about 13% of the dataset. Most lakes here sit in C or D — productive, often shallow, frequently algal in late summer.
The state's lakes lean eutrophic: enough nutrient input to support an active algal community, with the trade-offs in clarity and dissolved oxygen that come with it. Pennington ranks highest on average county grade (A). Roberts sits lowest. With only 13 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.
Lake Map
Reservoirs in Wisconsin
View all 3 reservoirs →3 of 16 Wisconsin lakes (19%) are man-made reservoirs in the USACE National Inventory of Dams. 3 carry a High or Significant hazard rating. The oldest matched dam dates to 1954.
EPA-Impaired Lakes in Wisconsin
View all 1 impaired lakes →1 of 16 Wisconsin lakes (6%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle.
Counties
Top 25 Cleanest Lakes
| Rank | Lake | County | Grade | Clarity | Max Depth |
|---|---|---|---|---|---|
| 1 | Canyon Lake | Pennington | A | - | - |
| 2 | Oahlk1073a Lake | Hughes | A | 14 ft | - |
| 3 | Oahlk1110dw Lake | Sully | B | 12.8 ft | - |
| 4 | Oahlk1153dw Lake | Dewey | B | 11.4 ft | - |
| 5 | Oahlk1196dw Lake | Walworth | B | 7.5 ft | - |
| 6 | Bbdlk0987a Lake | Lyman | B | 4.7 ft | - |
| 7 | Ftrlk0880a Lake | Charles Mix | B | 5.8 ft | - |
| 8 | Bbdlk1055dw Lake | Stanley | C | 0.8 ft | - |
| 9 | Ftrlk0968dw Lake | Brule | C | 1.7 ft | - |
| 10 | Ftrlk0911dw Lake | Gregory | C | 3.8 ft | - |
| 11 | Ftrlk0940dw Lake | Brule | C | 0.7 ft | - |
| 12 | Gptlk0811a Lake | Yankton | D | 2.4 ft | - |
| 13 | Gptlk0819dw Lake | Bon Homme | D | 1.3 ft | - |
| 14 | Lake Andes | Charles Mix | D | - | - |
| 15 | Traverse Lake | Roberts | D | 3.9 ft | - |
| 16 | Big Stone Lake | Roberts | F | 3 ft | - |
25 Lakes Needing Attention
| Rank | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | Big Stone Lake | Roberts | F | 3 ft |
| 2 | Traverse Lake | Roberts | D | 3.9 ft |
| 3 | Lake Andes | Charles Mix | D | - |
| 4 | Gptlk0819dw Lake | Bon Homme | D | 1.3 ft |
| 5 | Gptlk0811a Lake | Yankton | D | 2.4 ft |
| 6 | Ftrlk0940dw Lake | Brule | C | 0.7 ft |
| 7 | Ftrlk0911dw Lake | Gregory | C | 3.8 ft |
| 8 | Ftrlk0968dw Lake | Brule | C | 1.7 ft |
| 9 | Bbdlk1055dw Lake | Stanley | C | 0.8 ft |
| 10 | Ftrlk0880a Lake | Charles Mix | B | 5.8 ft |
| 11 | Bbdlk0987a Lake | Lyman | B | 4.7 ft |
| 12 | Oahlk1196dw Lake | Walworth | B | 7.5 ft |
| 13 | Oahlk1153dw Lake | Dewey | B | 11.4 ft |
| 14 | Oahlk1110dw Lake | Sully | B | 12.8 ft |
| 15 | Oahlk1073a Lake | Hughes | A | 14 ft |
| 16 | Canyon Lake | Pennington | A | - |
Source: EPA National Aquatic Resource Surveys, 2026.