Wisconsin Lake Water Quality
Water quality grades for 130 monitored lakes across 59 counties.
Only about 10% of Indiana's lakes pull an A grade — the smaller, agricultural-watershed lakes that dominate the dataset tend to carry persistent nutrient loads. 48% of lakes fall in the D or F brackets.
Eutrophic conditions dominate — nutrient-loaded, productive, with algal pressure that shows up most years in late summer. These lakes tend to be shallow, agricultural-watershed, and over-warmed by the time July ends. The cleanest county on average is Clay (grade A); the most-stressed is Huntington. The gap between the top and bottom counties is large enough that "Indiana lake water quality" hides real local variation.
Lake Map
Reservoirs in Wisconsin
View all 49 reservoirs →49 of 130 Wisconsin lakes (38%) are man-made reservoirs in the USACE National Inventory of Dams. 47 carry a High or Significant hazard rating. The oldest matched dam dates to 1835.
EPA-Impaired Lakes in Wisconsin
View all 49 impaired lakes →49 of 130 Wisconsin lakes (38%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 1 have an approved Total Maximum Daily Load (TMDL) restoration plan.
Counties
Top 25 Cleanest Lakes
| Rank | Lake | County | Grade | Clarity | Max Depth |
|---|---|---|---|---|---|
| 1 | Wbu-07 Lake | Clay | A | 18.9 ft | - |
| 2 | Umk-02 Lake | LaPorte | A | 15.5 ft | - |
| 3 | Wel-01 Lake | Washington | A | 15.6 ft | - |
| 4 | Middle Lagoon Lake | Lake | A | - | - |
| 5 | Wwl-06 Lake | Sullivan | A | 10.3 ft | - |
| 6 | Umk-04 Lake | LaPorte | A | 12.8 ft | - |
| 7 | Wae-01 Lake | Whitley | A | 11.3 ft | - |
| 8 | Wwu-11 Lake | Boone | A | 10.7 ft | - |
| 9 | Wem-09 Lake | Washington | A | 13 ft | - |
| 10 | Wed-01 Lake | Henry | A | 14.5 ft | - |
| 11 | Wem-08 Lake | Washington | A | 10 ft | - |
| 12 | Wde-01 Lake | Cass | A | 12.3 ft | - |
| 13 | Lej020 Lake | Steuben | A | 10.7 ft | - |
| 14 | Lmj-11 Lake | LaGrange | B | 9.3 ft | - |
| 15 | Lmg-02 Lake | LaPorte | B | 6.6 ft | - |
| 16 | Lake George | Steuben | B | 14.5 ft | - |
| 17 | Lmj-08 Lake | LaGrange | B | 9.8 ft | - |
| 18 | Lmj-08 Lake | Steuben | B | 7.4 ft | - |
| 19 | Lmj-07 Lake | Steuben | B | 9 ft | - |
| 20 | Wwu-17 Lake | Monroe | B | 7.5 ft | - |
| 21 | Dewart Lake | Kosciusko | B | 10.2 ft | - |
| 22 | Oswego Lake | Kosciusko | B | 9.9 ft | - |
| 23 | Wwu180 Lake | Monroe | B | 8.5 ft | - |
| 24 | Wti-06 Lake | Starke | B | 10.2 ft | - |
| 25 | Grand Calumet Lagoon Lake | Lake | B | - | - |
25 Lakes Needing Attention
| Rank | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | Wlv180 Lake | Parke | F | 1.5 ft |
| 2 | Wed-07 Lake | Johnson | F | 3.3 ft |
| 3 | Wem-07 Lake | Jennings | F | 2.8 ft |
| 4 | Wmi-06 Lake | Miami | F | 3.1 ft |
| 5 | Wwu-08 Lake | Hamilton | F | 3.1 ft |
| 6 | Lake Lemon | Monroe | F | 2.1 ft |
| 7 | Wel-11 Lake | Martin | F | 1.7 ft |
| 8 | Wti060 Lake | Fulton | F | 2.5 ft |
| 9 | Waw-01 Lake | Howard | F | 1.5 ft |
| 10 | Wsu-06 Lake | Montgomery | F | 1.8 ft |
| 11 | Weu-05 Lake | Jackson | F | 0.8 ft |
| 12 | Wae-02 Lake | Allen | F | 2.3 ft |
| 13 | Gmw-04 Lake | Fayette | F | 3.1 ft |
| 14 | Wem-04 Lake | Jennings | F | 1.5 ft |
| 15 | Ohp-06 Lake | Posey | F | 0.5 ft |
| 16 | Umk-03 Lake | St. Joseph | F | 2.6 ft |
| 17 | Wwl-10 Lake | Pike | F | 1.8 ft |
| 18 | Olp-09 Lake | Spencer | F | 1.6 ft |
| 19 | Olp-09 Lake | Dubois | F | 1.7 ft |
| 20 | Wti-04 Lake | Kosciusko | F | 3.1 ft |
| 21 | Wae-05 Lake | Kosciusko | F | 2.5 ft |
| 22 | Wuw-06 Lake | Wells | F | 3.3 ft |
| 23 | Big Barbee Lake | Kosciusko | F | 3.1 ft |
| 24 | Beaver Dam Lake | Kosciusko | F | 3.1 ft |
| 25 | Pike Lake | Kosciusko | F | 1.9 ft |
Source: EPA National Aquatic Resource Surveys, 2026.