Impaired Lakes in Wisconsin
94 of 185 graded Wisconsin lakes (51%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 30 have an approved TMDL restoration plan.
Top Causes of Impairment in Wisconsin
All 94 EPA-Listed Impaired Lakes in Wisconsin
| Lake | County | Grade | Causes | TMDL |
|---|---|---|---|---|
| Blue Mtn Lake | Hamilton | A | Mercury | ✓ |
| Brant Lake | Warren | A | Oxygen depletion (low DO) | — |
| Oquaga Lake | Broome | A | Nutrients (phosphorus, nitrogen) | — |
| Chenango Lake | Chenango | A | Oxygen depletion (low DO) | — |
| Lincoln Pond | Essex | A | Mercury | ✓ |
| Lake Moraine | Madison | A | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | — |
| Burden Lake | Rensselaer | A | Oxygen depletion (low DO) | — |
| Brant Lake | Warren | A | Oxygen depletion (low DO) | — |
| China Pond | Putnam | A | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Song Lake | Cortland | A | Oxygen depletion (low DO) | — |
| Indian Lake | Putnam | A | Nutrients (phosphorus, nitrogen) | — |
| Eaton Reservoir | Madison | A | Oxygen depletion (low DO) | — |
| Canadice Lake | Ontario | A | PCBs | — |
| Cazenovia Lake | Madison | A | Nutrients (phosphorus, nitrogen) | — |
| West Pond | Herkimer | A | pH / acidity | — |
| Little Clear Pond | Franklin | A | pH / acidity | ✓ |
| Squash Pond | Herkimer | A | pH / acidity, Salinity / chlorides | ✓ |
| Windfall Pond | Herkimer | A | pH / acidity | ✓ |
| Loon Hollows Pond | Herkimer | A | pH / acidity | ✓ |
| Grass Pond | Franklin | A | pH / acidity | ✓ |
| Willys Lake | Herkimer | A | pH / acidity | ✓ |
| Barnes Lake | Lewis | A | pH / acidity | — |
| Main Section Lake | Clinton | A | Mercury, Nutrients (phosphorus, nitrogen), PCBs | ✓ |
| Sodus Bay Lake | Wayne | B | Nutrients (phosphorus, nitrogen) | — |
| Conesus Lake | Livingston | B | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | ✓ |
| Schroon Lake | Essex | B | Mercury | ✓ |
| Taconic Pond | Rensselaer | B | Mercury | ✓ |
| Cuba Lake | Allegany | B | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | — |
| Robinson Pond | Columbia | B | Nutrients (phosphorus, nitrogen) | — |
| Crooked Lake | Onondaga | B | Oxygen depletion (low DO) | — |
| Upper Little York Lake | Cortland | B | Oxygen depletion (low DO) | — |
| Barrett Pond | Putnam | B | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Guilford Lake | Chenango | B | Nutrients (phosphorus, nitrogen) | — |
| Canada Lake | Fulton | B | Mercury | ✓ |
| Little Long Pond | Suffolk | B | Pathogens (E. coli, fecal) | ✓ |
| Fulton Chain Lakes | Herkimer | B | Pesticides | — |
| Owasco Lake | Cayuga | B | Pathogens (E. coli, fecal) | — |
| Montgomery Lake | Sullivan | B | Nutrients (phosphorus, nitrogen) | — |
| Saratoga Lake | Saratoga | B | Nutrients (phosphorus, nitrogen) | — |
| Tully Lake | Cortland | B | Oxygen depletion (low DO) | — |
| Irondequoit Bay Lake | Monroe | C | Pesticides, PCBs | — |
| Honeoye Lake | Ontario | C | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | ✓ |
| Lime Lake | Cattaraugus | C | Nutrients (phosphorus, nitrogen) | — |
| Sepasco Lake | Dutchess | C | Nutrients (phosphorus, nitrogen) | — |
| Cossayuna Lake | Washington | C | Nutrients (phosphorus, nitrogen) | ✓ |
| Lake Como | Cayuga | C | Nutrients (phosphorus, nitrogen) | — |
| Forest Lake | Rensselaer | C | Mercury | ✓ |
| Big Fresh Pond | Suffolk | C | Nutrients (phosphorus, nitrogen) | — |
| Oscaleta Lake | Westchester | C | Nutrients (phosphorus, nitrogen) | — |
| Silver Lake | Wyoming | C | Nutrients (phosphorus, nitrogen) | ✓ |
| Lamoka Lake | Schuyler | C | Oxygen depletion (low DO) | — |
| Roaring Brook Lake | Putnam | C | Metals (other than mercury) | — |
| Peach Lake | Putnam | C | Nutrients (phosphorus, nitrogen), Pathogens (E. coli, fecal) | ✓ |
| Findley Lake | Chautauqua | C | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | ✓ |
| Augur Lake | Essex | C | Nutrients (phosphorus, nitrogen) | — |
| Irondequoit Bay Lake | Monroe | D | Pesticides, PCBs | — |
| Pleasure Lake | Sullivan | D | Nutrients (phosphorus, nitrogen) | — |
| Fresh Pond | Suffolk | D | Nutrients (phosphorus, nitrogen) | — |
| Palmer Lake | Putnam | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Duck Lake | Cayuga | D | Nutrients (phosphorus, nitrogen) | — |
| Eagle Pond | Franklin | D | pH / acidity | — |
| Otisco Lake | Onondaga | D | Oxygen depletion (low DO) | — |
| Ballston Lake | Saratoga | D | Nutrients (phosphorus, nitrogen) | — |
| Deer Lake | Broome | D | Nutrients (phosphorus, nitrogen) | — |
| Long Pond | Suffolk | D | Pathogens (E. coli, fecal) | ✓ |
| Smith Pond | Steuben | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Salubria | Steuben | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Lake Mohegan | Westchester | D | Nutrients (phosphorus, nitrogen) | — |
| Kirk Lake | Putnam | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Rippowam | Westchester | D | Nutrients (phosphorus, nitrogen) | — |
| Sodus Bay Lake | Wayne | D | Nutrients (phosphorus, nitrogen) | — |
| Little Fresh Pond | Suffolk | D | Nutrients (phosphorus, nitrogen) | — |
| Otter Lake | Oneida | D | pH / acidity | — |
| Lake Peekskill | Putnam | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Tibet | Putnam | D | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Lake Waccabuc | Westchester | D | Ammonia, Nutrients (phosphorus, nitrogen) | — |
| Barger Pond | Putnam | D | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | — |
| Pleasant Lake | Oswego | D | Nutrients (phosphorus, nitrogen) | — |
| Waneta Lake | Schuyler | D | Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) | — |
| Kinderhook Lake | Columbia | D | Nutrients (phosphorus, nitrogen), PCBs | ✓ |
| Sleepy Hollow Lake | Greene | D | Nutrients (phosphorus, nitrogen) | — |
| Plymouth Reservoir | Chenango | D | Nutrients (phosphorus, nitrogen) | — |
| Seven Hills Lake | Putnam | D | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Lake Carmel | Putnam | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Duane Lake | Schenectady | D | Nutrients (phosphorus, nitrogen) | — |
| Stissing Pond | Dutchess | D | Nutrients (phosphorus, nitrogen) | — |
| Lk Ontario Lake | Monroe | D | Nutrients (phosphorus, nitrogen) | — |
| Orange Lake | Orange | F | Nutrients (phosphorus, nitrogen) | — |
| Lake Lincolndale | Westchester | F | Nutrients (phosphorus, nitrogen) | — |
| Howlands Lake | Westchester | F | Nutrients (phosphorus, nitrogen) | — |
| Deer River Flow Lake | Franklin | F | pH / acidity | — |
| Lake Lacoma | Monroe | F | Nutrients (phosphorus, nitrogen) | — |
| Java Lake | Wyoming | F | Nutrients (phosphorus, nitrogen) | ✓ |
| Lake Lucille | Rockland | F | Nutrients (phosphorus, nitrogen) | — |
Frequently Asked Questions
How many lakes are impaired in Wisconsin?
94 of 185 graded Wisconsin lakes (51%) are listed as impaired in the most recent EPA ATTAINS reporting cycle. Of those, 72 are on the federal Clean Water Act §303(d) list and 30 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) (58 lakes); Oxygen depletion (low DO) (18 lakes); Mercury (11 lakes); pH / acidity (11 lakes); PCBs (5 lakes); Pathogens (E. coli, fecal) (4 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.