Impaired Lakes in Wisconsin
41 of 158 graded Wisconsin lakes (26%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 20 have an approved TMDL restoration plan.
Top Causes of Impairment in Wisconsin
All 41 EPA-Listed Impaired Lakes in Wisconsin
| Lake | County | Grade | Causes | TMDL |
|---|---|---|---|---|
| Whitman Dam Lake | Nelson | B | Nutrients (phosphorus, nitrogen) | — |
| Patterson Lake | Stark | B | Nutrients (phosphorus, nitrogen), Sediment / turbidity, Turbidity | ✓ |
| Lake Ashtabula | Barnes | B | Nutrients (phosphorus, nitrogen) | — |
| Northgate Dam Lake | Burke | B | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | ✓ |
| Jamestown Reservoir | Stutsman | B | Nutrients (phosphorus, nitrogen) | — |
| Pheasant Lake | Dickey | B | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | ✓ |
| Blacktail Dam Lake | Williams | B | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | ✓ |
| Homme Dam Lake | Walsh | B | Nutrients (phosphorus, nitrogen), Sediment / turbidity | ✓ |
| Carlson-Tande Dam Lake | Griggs | C | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | — |
| Fordville Dam Lake | Grand Forks | C | Nutrients (phosphorus, nitrogen) | ✓ |
| Mooreton Pond | Richland | C | Salinity / chlorides | — |
| Powers Lake | Mountrail | C | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO), Sediment / turbidity | ✓ |
| Short Creek Dam Lake | Burke | C | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | ✓ |
| Lake Tschida | Grant | C | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Lake Tschida | Grant | C | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Beaver Lake | Logan | C | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO), Sediment / turbidity | — |
| Renwick Dam Lake | Pembina | C | Nutrients (phosphorus, nitrogen), Sediment / turbidity | — |
| Mcville Dam Lake | Nelson | C | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO), Sediment / turbidity | — |
| Armourdale Dam Lake | Towner | C | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | ✓ |
| Devils Lake | Ramsey | C | Mercury | — |
| Powers Lake Dredge Site | Mountrail | C | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO), Sediment / turbidity | ✓ |
| Lake Tschida | Grant | C | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Lake Tschida | Grant | C | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Lake Darling | Renville | C | Nutrients (phosphorus, nitrogen) | — |
| Larson Lake | Hettinger | C | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | — |
| Indian Creek Dam Lake | Hettinger | C | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | ✓ |
| Bowman-Haley Dam Lake | Bowman | C | Nutrients (phosphorus, nitrogen) | — |
| E. A. Patterson Lake | Stark | D | Nutrients (phosphorus, nitrogen), Sediment / turbidity, Turbidity | ✓ |
| Larimore Dam Lake | Grand Forks | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Mcdowell Dam Lake | Burleigh | D | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | ✓ |
| Sheep Creek Dam Lake | Grant | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Stanley Reservoir | Mountrail | D | Nutrients (phosphorus, nitrogen) | — |
| Brewer Lake | Cass | D | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO), Sediment / turbidity | ✓ |
| Warsing Dam Lake | Eddy | D | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO), Sediment / turbidity | — |
| Buffalo Lake | Pierce | F | Nutrients (phosphorus, nitrogen) | — |
| Dead Colt Creek Dam Lake | Ransom | F | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | ✓ |
| Sweetbriar Dam Lake | Morton | F | Nutrients (phosphorus, nitrogen) | ✓ |
| Sweet Briar Dam-Mid Reservoir | Morton | F | Nutrients (phosphorus, nitrogen) | ✓ |
| Cedar Lake | Slope | F | Sediment / turbidity | — |
| Mirror Lake | Adams | F | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | ✓ |
| Kolding Dam Lake | Grand Forks | F | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | — |
Frequently Asked Questions
How many lakes are impaired in Wisconsin?
41 of 158 graded Wisconsin lakes (26%) are listed as impaired in the most recent EPA ATTAINS reporting cycle. Of those, 25 are on the federal Clean Water Act §303(d) list and 20 have an approved Total Maximum Daily Load (TMDL) restoration plan.
What does Clean Water Act §303(d) mean?
Section 303(d) of the federal Clean Water Act requires every state to identify waters that don't meet water quality standards even after pollution control measures. Each listed water must then have a Total Maximum Daily Load (TMDL) developed — a plan that caps how much of each pollutant can enter the waterbody. The "303(d) list" is the impaired-waters list. The EPA reviews each state's list every two years.
What are the top causes of impairment in Wisconsin?
The most common causes flagged across Wisconsin's impaired lakes are: Nutrients (phosphorus, nitrogen) (38 lakes); Oxygen depletion (low DO) (18 lakes); Sediment / turbidity (11 lakes); Mercury (5 lakes); Turbidity (2 lakes); Salinity / chlorides (1 lakes). Mercury is widespread in fish tissue across the upper Midwest from atmospheric deposition. Nutrient impairment (phosphorus, nitrogen) typically reflects agricultural runoff and urban stormwater.
Can I swim in an impaired lake?
It depends on the cause of impairment. A lake impaired for "mercury in fish tissue" is generally safe to swim in — the warning is about long-term consumption of fish. A lake impaired for "pathogens" (E. coli) or "algal growth" may pose a swimming risk and often has a separate beach advisory. Check the cause categories listed for each lake below, and consult your state health department's beach monitoring program for current advisories.
Where does this impairment data come from?
Every impairment record on this page comes from the EPA's ATTAINS (Assessment and TMDL Tracking and Implementation System) public dataset, the federal repository of state-reported water quality assessments. EPA ATTAINS is published as GeoParquet files on the EPA Office of Water S3 bucket and refreshed several times per year. Causes and use-support codes follow EPA's standard taxonomy.
Data source
Impairment data from the EPA ATTAINS (Assessment and TMDL Tracking and Implementation System) public dataset. Assessment unit IDs are matched to LakeGrade waterbodies by name and proximity; some lakes may not appear here if their ATTAINS name doesn't match our naming convention. For an official query, consult Wisconsin's state water-quality agency.