Impaired Lakes in Wisconsin
518 of 1,422 graded Wisconsin lakes (36%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 77 have an approved TMDL restoration plan.
Top Causes of Impairment in Wisconsin
296
Nutrients (phosphorus, nitrogen)
134
Mercury
89
Cause unknown
26
PCBs
17
Metals (other than mercury)
15
Turbidity
13
Pathogens (E. coli, fecal)
5
PFAS
Reading the Wisconsin impairment landscape
Wisconsin reports 518 impaired lakes — 36% of the state's 1,422 tracked water bodies. That share is high enough to make impairment a meaningful planning concern: roughly one in four lakes carries at least one §303(d) listing for a pollutant exceeding standards. The list below isn't a niche concern — it's a significant chunk of the state's surface-water inventory.
The leading impairment category in Wisconsin is Nutrients (phosphorus, nitrogen) — nutrient enrichment, typically from agricultural fertilizer runoff, septic discharge, or stormwater carrying lawn-care residue. Nutrient-impaired lakes can still be safe for contact recreation in many conditions, but they're prone to algal blooms (including potentially toxic cyanobacteria) during warm-water periods. Check the state's beach-monitoring or harmful-algal-bloom dashboard before swimming on nutrient-impaired waters in summer.
Impaired-waters listings come from the state environmental agency's §303(d) submission to EPA, refreshed on a roughly 2-year cycle. A listed lake stays on the list until either a TMDL is established and the cleanup completes, or subsequent monitoring shows the pollutant concentrations no longer exceed water-quality standards. The list below reflects the most recent available Wisconsin submission to the EPA Assessment, Total Maximum Daily Load Tracking and Implementation System (ATTAINS) dataset.
All 518 EPA-Listed Impaired Lakes in Wisconsin
| Lake | County | Grade | Causes | TMDL |
|---|---|---|---|---|
| Beasley Lake | Waupaca | A | Nutrients (phosphorus, nitrogen) | — |
| Sugar Camp Lake | Oneida | A | Mercury | — |
| Round Lake | Waupaca | A | Nutrients (phosphorus, nitrogen) | — |
| Clear Lake | Oneida | A | Mercury | — |
| Pike Lake | Polk | A | Nutrients (phosphorus, nitrogen) | — |
| Hemlock Lake | Oneida | A | Mercury | — |
| White Lake | Oconto | A | Nutrients (phosphorus, nitrogen) | — |
| Alva Lake | Oneida | A | Mercury | — |
| Franklin Lake | Oneida | A | Mercury | — |
| Sand Lake | Rusk | A | Mercury | — |
| Crystal Lake | Bayfield | A | Mercury | — |
| Crystal Lake | Sheboygan | A | Mercury | — |
| Perch Lake | Oneida | A | Mercury | — |
| White Birch Lake | Vilas | A | Mercury | — |
| Paddock Lake | Kenosha | A | Nutrients (phosphorus, nitrogen) | — |
| Sunset Lake | Vilas | A | Nutrients (phosphorus, nitrogen) | — |
| Ballard Lake | Vilas | A | Mercury | — |
| Mary Lake | Lincoln | A | Mercury | — |
| Moose Lake | Waukesha | A | Nutrients (phosphorus, nitrogen) | — |
| Dorothy Lake | Oneida | A | Mercury | — |
| Bird Lake | Oneida | A | Mercury | — |
| Buffalo Lake | Oneida | A | Nutrients (phosphorus, nitrogen) | — |
| Clear Lake | Rock | A | Cause unknown | — |
| Pope Lake | Waupaca | A | Nutrients (phosphorus, nitrogen) | — |
| Middle Mckenzie Lake | Burnett | A | Nutrients (phosphorus, nitrogen) | — |
| Clara Lake-Deep Hole | Lincoln | A | Mercury | — |
| Hodstradt Lake | Oneida | A | Mercury | — |
| Arbutus Lake | Forest | A | Cause unknown | — |
| Lake Buteau | Lincoln | A | Mercury | — |
| Slim Lake | Washburn | A | Nutrients (phosphorus, nitrogen) | — |
| Hewitt Lake | Iron | A | Mercury | — |
| Heidmann Lake | Kewaunee | A | Nutrients (phosphorus, nitrogen) | ✓ |
| Day Lake | Vilas | A | Mercury | — |
| Round Lake Northeast Site | Chippewa | A | Mercury | — |
| Nc Cheq Bay Lake | Ashland | A | Toxic organics | — |
| Trego Lake | Washburn | A | Cause unknown | — |
| Tambling Lake | Vilas | A | Cause unknown | — |
| Greater Bass Lake | Langlade | A | Mercury | — |
| Lac Courte Oreilles Lake | Sawyer | A | Cause unknown | — |
| Whitefish Lake | Sawyer | A | Mercury | — |
| Big Cedar Lake-South Site-Near West Bend | Washington | A | Cause unknown | — |
| Lake Beulah | Walworth | A | Nutrients (phosphorus, nitrogen) | — |
| Okauchee Lake | Waukesha | A | Nutrients (phosphorus, nitrogen) | — |
| Silver Lake | Barron | A | Mercury | — |
| Silver Lake | Vilas | A | Cause unknown | — |
| Mirror Lake | Waupaca | A | Cause unknown | — |
| Bass Lake | Barron | A | Nutrients (phosphorus, nitrogen) | — |
| Bass Lake | Vilas | A | Cause unknown | — |
| Bass Lake | Lincoln | A | Mercury | — |
| Marl Lake | Waupaca | A | Nutrients (phosphorus, nitrogen) | — |
| Indian Lake | Oneida | A | Mercury | — |
| Spider Lake | Vilas | A | Nutrients (phosphorus, nitrogen) | — |
| Round Lake | Shawano | A | Cause unknown | ✓ |
| Clear Lake | Rusk | A | Nutrients (phosphorus, nitrogen) | — |
| Long Lake | Waupaca | A | Nutrients (phosphorus, nitrogen) | — |
| Long Lake | Lincoln | A | Mercury | — |
| Shadow Lake | Waupaca | A | Cause unknown | — |
| Crescent Lake | Oneida | A | Mercury | — |
| Red Cedar Lake | Barron | A | Nutrients (phosphorus, nitrogen) | — |
| Pipe Lake | Polk | A | Mercury | — |
| Armour Lake | Vilas | A | Mercury | — |
| Big Dummy Lake | Barron | A | Nutrients (phosphorus, nitrogen) | — |
| Diamond Lake | Bayfield | A | Mercury | — |
| Echo Lake | Barron | A | Cause unknown | — |
| Church Pine Lake | Polk | A | Nutrients (phosphorus, nitrogen) | — |
| Wind Lake | Polk | A | Nutrients (phosphorus, nitrogen) | — |
| Oconomowoc Lake Site | Waukesha | A | Nutrients (phosphorus, nitrogen) | — |
| Tahkodah Lake | Bayfield | A | Mercury | — |
| Meta Lake | Vilas | A | Cause unknown | — |
| Forest Lake | Fond du Lac | A | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Turtle Lake | Walworth | A | Cause unknown | — |
| Maple Lake | Oneida | A | Mercury | — |
| Korth Lake | Shawano | A | Cause unknown | — |
| Horsehead Lake | Vilas | A | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Windigo Lake | Sawyer | A | Mercury | — |
| Lynx Lake | Vilas | A | Mercury | — |
| Seven Island Lake | Lincoln | A | Mercury | — |
| Snipe Lake | Vilas | A | Mercury | — |
| Pine Lake | Shawano | A | Cause unknown | ✓ |
| Moon Lake | Vilas | A | Nutrients (phosphorus, nitrogen) | — |
| Fowler Lake | Waukesha | A | Nutrients (phosphorus, nitrogen), PCBs | — |
| Spirit Lake | Oneida | A | Mercury | — |
| Columbia Lake | Waupaca | A | Nutrients (phosphorus, nitrogen) | — |
| Gilmore Lake | Washburn | A | Nutrients (phosphorus, nitrogen) | — |
| Elkhart Lake | Sheboygan | A | Mercury | — |
| Lake Beulah | Walworth | A | Nutrients (phosphorus, nitrogen) | — |
| Alma Lake | Vilas | A | Nutrients (phosphorus, nitrogen) | — |
| Axhandle Lake | Chippewa | A | Mercury | — |
| Irving Lake | Vilas | A | Mercury | — |
| Tuma Lake | Manitowoc | A | Nutrients (phosphorus, nitrogen) | ✓ |
| Finger Lake | Vilas | A | Cause unknown | — |
| Okauchee Lake | Waukesha | A | Nutrients (phosphorus, nitrogen) | — |
| Antler Lake | Polk | A | Nutrients (phosphorus, nitrogen) | — |
| Hunter Lake | Vilas | A | Nutrients (phosphorus, nitrogen) | — |
| Lone Stone Lake | Oneida | A | Mercury | — |
| Big Mckenzie Lake | Washburn | A | Nutrients (phosphorus, nitrogen) | — |
| De Neveu Lake | Fond du Lac | A | Nutrients (phosphorus, nitrogen) | — |
| Upper Gresham Lake | Vilas | A | Mercury | — |
| Little Dummy Lake | Barron | A | Nutrients (phosphorus, nitrogen) | — |
| Little Cedar Lake | Washington | A | Cause unknown | — |
| Hilbert Lake | Marinette | A | Cause unknown | — |
| Taylor Lake | Waupaca | A | Nutrients (phosphorus, nitrogen) | ✓ |
| Sand Lake | Sawyer | B | Mercury | — |
| Green Lake | Green Lake | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Pickerel Lake | Forest | B | Cause unknown | — |
| Pickerel Lake | Lincoln | B | Mercury | — |
| North Turtle Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Balsam Lake | Washburn | B | Nutrients (phosphorus, nitrogen) | — |
| Cedar Lake | Iron | B | Mercury | — |
| Deep Lake | Washburn | B | Nutrients (phosphorus, nitrogen) | — |
| Bass Lake | Price | B | Mercury | — |
| Oxbow Lake | Vilas | B | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Spider Lake | Iron | B | Mercury | — |
| Whitefish Lake | Oneida | B | Mercury | — |
| Round Lake | Chippewa | B | Mercury | — |
| Round Lake | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Pioneer Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Long Lake | Washburn | B | Nutrients (phosphorus, nitrogen) | — |
| Long Lake | Oneida | B | Mercury | — |
| North Lake | Waukesha | B | Nutrients (phosphorus, nitrogen) | — |
| Camelot Lake | Adams | B | Cause unknown | — |
| Saint Croix Flowage Lake | Douglas | B | Mercury | — |
| Island Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Stone Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Grass Lake | Shawano | B | Cause unknown | ✓ |
| Little Sand Lake | Forest | B | Mercury | — |
| Walsh Lake | Forest | B | Mercury | — |
| Little Pine Lake | Iron | B | Mercury | — |
| Sand Lake | Barron | B | Cause unknown | — |
| Sand Lake | Iron | B | Mercury | — |
| Sand Lake | Florence | B | Mercury | — |
| Lower Vermillion Lake | Barron | B | Cause unknown | — |
| Annabelle Lake | Vilas | B | Mercury | — |
| Schnur Lake | Price | B | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Beaver Lake | Chippewa | B | Nutrients (phosphorus, nitrogen) | — |
| Pensaukee Lake | Shawano | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Virgin Lake | Oneida | B | Mercury | — |
| Lake Nebagamon | Douglas | B | Mercury | — |
| Youngs Lake Waupaca Co | Waupaca | B | Nutrients (phosphorus, nitrogen) | — |
| Otter Lake | Waupaca | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Big Moon Lake at | Barron | B | Nutrients (phosphorus, nitrogen) | — |
| Porcupine Lake | Oconto | B | Nutrients (phosphorus, nitrogen) | — |
| Hill Lake | Oneida | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Camelot Lake | Adams | B | Cause unknown | — |
| Durphee Lake | Sawyer | B | Cause unknown | — |
| Lake Julia | Oneida | B | Mercury | — |
| Freedom Lakes | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Lamont Lake | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Lower Phantom Lake | Waukesha | B | Nutrients (phosphorus, nitrogen) | — |
| Shannon Lake | Vilas | B | Mercury | — |
| Mccullough Lake | Vilas | B | Cause unknown | — |
| Dads Lake | Vilas | B | Cause unknown | — |
| Big Cedar Lake | Washington | B | Cause unknown | — |
| Army Lake | Walworth | B | Nutrients (phosphorus, nitrogen) | — |
| Long Lake -Spread Eagle Chain | Florence | B | Mercury | — |
| Little Carr Lake | Oneida | B | Mercury | — |
| Big Carr Lake | Oneida | B | Mercury | — |
| Green Lake | Green Lake | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Cross Lake | Kenosha | B | Nutrients (phosphorus, nitrogen) | — |
| Morton Lake | Vilas | B | Cause unknown | — |
| Prong Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Mcnutt Lake | Oneida | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Oneonta Lake | Marinette | B | Cause unknown | — |
| L St Germain Lk Site K @ S. Bay Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Siskiwit Lake | Bayfield | B | Mercury | — |
| Delavan Lake | Walworth | B | Nutrients (phosphorus, nitrogen) | — |
| Little Rice Lake | Forest | B | Mercury | — |
| Siskiwit Lake | Bayfield | B | Mercury | — |
| East Wetland Inlet To Lake Ree | Bayfield | B | Mercury | — |
| Calkins Lake | Chippewa | B | Mercury | — |
| Dace Lake | Polk | B | Cause unknown | — |
| Green Lake | Green Lake | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Delavan Lake | Walworth | B | Nutrients (phosphorus, nitrogen) | — |
| Delavan Lake | Walworth | B | Nutrients (phosphorus, nitrogen) | — |
| Green Lake | Green Lake | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Lake St. Croix | St. Croix | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Balsam Lake | Polk | B | Cause unknown | — |
| Silver Lake | Columbia | B | Mercury, Metals (other than mercury), PCBs | — |
| Little Friess Lake | Washington | B | Cause unknown | — |
| Bone Lake | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Turtle Flambeau Flowage Lake | Iron | B | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Bear Lake | Forest | B | Cause unknown | — |
| Bear Lake | Barron | B | Nutrients (phosphorus, nitrogen) | — |
| Rainbow Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Crescent Lake | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Island Lake | Oneida | B | Mercury | — |
| Lac la Belle Lake | Waukesha | B | Nutrients (phosphorus, nitrogen), PCBs | — |
| Big Lake | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Mid Lake | Oneida | B | Mercury | — |
| Mcdonald Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Bahr Lake | Shawano | B | Cause unknown | — |
| Crane Lake | Forest | B | Cause unknown | — |
| Horseshoe Lake | Polk | B | Cause unknown | — |
| Auburn Lake | Fond du Lac | B | Mercury, Nutrients (phosphorus, nitrogen) | — |
| St Croix Flowage Lake | Douglas | B | Mercury | — |
| Spring Lake | Portage | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Beaver Lake | Vilas | B | Cause unknown | — |
| Robinson Pond | Jackson | B | Mercury | — |
| Pine Lake | Iron | B | Mercury | — |
| Lake Minnesuing | Douglas | B | Mercury | — |
| Loveless Lake | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Lipsett Lake | Burnett | B | Cause unknown | — |
| Big Bass Lake | Marathon | B | Mercury | — |
| Bear Trap Lake | Polk | B | Cause unknown | — |
| English Lake | Manitowoc | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Clarey Lake | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Van Zile Lake | Forest | B | Mercury | — |
| Silver Lake West Basin | Columbia | B | Mercury, Metals (other than mercury), PCBs | — |
| Black Hawk Lake | Iowa | B | Cause unknown | — |
| Lake Pesobic | Lincoln | B | Mercury | — |
| Little Bearskin Lake | Oneida | B | Cause unknown | — |
| Kasbaum Lake | Manitowoc | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Moccasin Lake | Oneida | B | Mercury | — |
| Mckenzie Lake | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Lake Thirty | Barron | B | Nutrients (phosphorus, nitrogen) | — |
| Lake Content | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Okauchee Lake Site | Waukesha | B | Nutrients (phosphorus, nitrogen) | — |
| Okauchee Lake Deep Hole Usgs | Waukesha | B | Nutrients (phosphorus, nitrogen) | — |
| Ocauchee Lake | Waukesha | B | Nutrients (phosphorus, nitrogen) | — |
| Delavan Lake | Walworth | C | Nutrients (phosphorus, nitrogen) | — |
| Pickerel Lake | Portage | C | Nutrients (phosphorus, nitrogen) | — |
| Pickerel Lake | Vilas | C | Cause unknown | — |
| Bass Lake | Oneida | C | Mercury | — |
| Townline Lake | Oneida | C | Mercury | — |
| Indian Lake | Oneida | C | Cause unknown | — |
| Milwaukee Harbor Lake | Milwaukee | C | Metals (other than mercury), Pathogens (E. coli, fecal), PCBs | ✓ |
| Round Lake | Price | C | Nutrients (phosphorus, nitrogen) | — |
| Round Lake | Oneida | C | Mercury | — |
| Chain Lake | Chippewa | C | Mercury | — |
| Long Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Long Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Long Lake | Shawano | C | Cause unknown | ✓ |
| Birch Lake | Oneida | C | Cause unknown | — |
| Birch Lake | Washburn | C | Nutrients (phosphorus, nitrogen) | — |
| Rock Lake | Vilas | C | Nutrients (phosphorus, nitrogen) | — |
| Delavan Lake | Walworth | C | Nutrients (phosphorus, nitrogen) | — |
| Wolf Lake | Portage | C | Nutrients (phosphorus, nitrogen) | — |
| Dog Lake | Oneida | C | Mercury | — |
| Green Lake | Green Lake | C | Nutrients (phosphorus, nitrogen) | ✓ |
| Nelson Lake | Sawyer | C | Nutrients (phosphorus, nitrogen) | — |
| Lakeshore State Park Fish Shocking | Milwaukee | C | Metals (other than mercury), Pathogens (E. coli, fecal), PCBs | ✓ |
| Deer Lake | Oneida | C | Mercury | — |
| Duck Lake | Langlade | C | Nutrients (phosphorus, nitrogen) | — |
| Bearskin Lake | Oneida | C | Cause unknown | — |
| Fawn Lake | Vilas | C | Nutrients (phosphorus, nitrogen) | — |
| Mud Lake | Polk | C | Cause unknown | — |
| Big Arbor Vitae Lake | Vilas | C | Nutrients (phosphorus, nitrogen) | — |
| Little Sand Lake | Barron | C | Cause unknown | — |
| Lake Esadore | Taylor | C | Mercury | — |
| Amnicon Lake | Douglas | C | Cause unknown, Turbidity | — |
| Stella Lake | Vilas | C | Mercury | — |
| Found Lake | Vilas | C | Cause unknown | — |
| Ward Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Whitewater Lake | Walworth | C | Nutrients (phosphorus, nitrogen) | — |
| Laurel Lake | Oneida | C | Mercury, Nutrients (phosphorus, nitrogen) | — |
| West Horsehead Lake | Oneida | C | Mercury | — |
| Wood Lake | Burnett | C | Nutrients (phosphorus, nitrogen) | — |
| Big Trade Lake | Burnett | C | Nutrients (phosphorus, nitrogen) | — |
| Hancock Lake | Oneida | C | Cause unknown | — |
| White Mound Lake | Sauk | C | Cause unknown | — |
| Shawano Lake | Shawano | C | Nutrients (phosphorus, nitrogen) | ✓ |
| Bullhead Lake | Langlade | C | Nutrients (phosphorus, nitrogen) | — |
| Big Stone Lake | Oneida | C | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Pine Lake | Forest | C | Cause unknown | — |
| Moon Lake | Barron | C | Nutrients (phosphorus, nitrogen) | — |
| Milwaukee Harbor Lake | Milwaukee | C | Metals (other than mercury), Pathogens (E. coli, fecal), PCBs | ✓ |
| Lake Sherwood | Adams | C | Cause unknown | — |
| Amacoy Lake | Rusk | C | Cause unknown | — |
| North Pipe Lake | Polk | C | Cause unknown | — |
| Milwaukee Harbor Lake | Milwaukee | C | Metals (other than mercury), Pathogens (E. coli, fecal), PCBs | ✓ |
| Enterprise Lake | Langlade | C | Cause unknown | — |
| Yellow Lake | Burnett | C | Nutrients (phosphorus, nitrogen) | — |
| Arrowhead Lake | Adams | C | Cause unknown | — |
| Collins Lake | Portage | C | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Granite Lake at | Barron | C | Cause unknown | — |
| Big Twin Lake | Green Lake | C | Nutrients (phosphorus, nitrogen) | ✓ |
| Tichigan Lake | Racine | C | PCBs | — |
| Red Bass Lake | Vilas | C | Nutrients (phosphorus, nitrogen) | — |
| Williams Lake | Marquette | C | PCBs | — |
| Easton Lake | Adams | C | Cause unknown | — |
| Oneida Lake | Oneida | C | Cause unknown | — |
| Voltz Lake | Kenosha | C | Nutrients (phosphorus, nitrogen) | — |
| Mineral Lake | Ashland | C | Nutrients (phosphorus, nitrogen) | — |
| Poskin Lake | Barron | C | Nutrients (phosphorus, nitrogen) | — |
| Swan Lake | Walworth | C | Nutrients (phosphorus, nitrogen) | — |
| High Falls Reservoir at | Marinette | C | Mercury | — |
| Twin Falls Flowage Us Twin Falls Dam Lake | Florence | C | Mercury | — |
| Little Fork Lake | Oneida | C | Mercury | — |
| Smith Lake | Vilas | C | Nutrients (phosphorus, nitrogen) | — |
| Range Line Lake | Vilas | C | Cause unknown | — |
| North Lake West Basin | Waukesha | C | Nutrients (phosphorus, nitrogen) | — |
| South Harper Lake | Taylor | C | Mercury | — |
| Lake Beulah | Walworth | C | Nutrients (phosphorus, nitrogen) | — |
| Little St. Germain Lk-South Bay-Nr St. Germain Lake | Vilas | C | Nutrients (phosphorus, nitrogen) | — |
| Lake Chetac North Basin | Sawyer | C | Nutrients (phosphorus, nitrogen) | — |
| Lake Lorraine | Walworth | C | Nutrients (phosphorus, nitrogen) | — |
| Potter Lake | Walworth | C | Nutrients (phosphorus, nitrogen) | — |
| Dowling Lake | Douglas | C | Cause unknown | — |
| Murdock Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Big Round Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Potter Lake | Walworth | C | Nutrients (phosphorus, nitrogen) | — |
| Cedar Lake | Polk | C | Nutrients (phosphorus, nitrogen) | ✓ |
| Hidden Valley Lake | Lafayette | C | Nutrients (phosphorus, nitrogen) | — |
| Cranberry Lake | Oneida | C | Cause unknown | — |
| Round Lake | Burnett | C | Nutrients (phosphorus, nitrogen) | — |
| Rice Lake | Barron | C | Nutrients (phosphorus, nitrogen) | — |
| Rice Lake | Vilas | C | Nutrients (phosphorus, nitrogen) | — |
| Lake Alice | Lincoln | C | Oxygen depletion (low DO) | — |
| Cooley Lake | Oconto | C | Nutrients (phosphorus, nitrogen) | — |
| Butternut Lake | Price | C | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Lake Emily | Dodge | C | Nutrients (phosphorus, nitrogen) | ✓ |
| Loon Lake | Chippewa | C | Mercury | — |
| Lake Puckaway | Green Lake | C | Cause unknown, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Hartlaub Lake | Manitowoc | C | Nutrients (phosphorus, nitrogen) | ✓ |
| Lake Mohawksin | Lincoln | C | Oxygen depletion (low DO), PFAS | — |
| Lake Desair | Barron | C | Nutrients (phosphorus, nitrogen), Turbidity | — |
| Little St Germain Lake | Vilas | C | Nutrients (phosphorus, nitrogen) | — |
| Porcupine Lake-Deep Hole | Oconto | C | Nutrients (phosphorus, nitrogen) | — |
| Lake Kegonsa | Dane | C | Nutrients (phosphorus, nitrogen), PFAS | ✓ |
| Milwaukee River Lake | Milwaukee | C | Metals (other than mercury), Pathogens (E. coli, fecal), PCBs | ✓ |
| Holcombe Flowage Lake | Chippewa | C | Nutrients (phosphorus, nitrogen), Turbidity | — |
| Fourmile Lake | Oneida | C | Mercury | — |
| Friess Lake | Washington | C | Nutrients (phosphorus, nitrogen) | — |
| White Clay Lake | Shawano | C | Nutrients (phosphorus, nitrogen) | ✓ |
| Horseshoe Lake | Manitowoc | C | Nutrients (phosphorus, nitrogen) | ✓ |
| Milwaukee Harbor North Half Lake | Milwaukee | C | Metals (other than mercury), Pathogens (E. coli, fecal), PCBs | ✓ |
| Upper Turtle Lake | Barron | C | Nutrients (phosphorus, nitrogen) | — |
| Milwaukee Harbor Lake | Milwaukee | C | Metals (other than mercury), Pathogens (E. coli, fecal), PCBs | ✓ |
| North Spirit Lake | Price | C | Cause unknown | — |
| Moose Lake | Sawyer | C | Mercury | — |
| Muskellunge Lake | Vilas | C | Cause unknown | — |
| Milwaukee Harbor Lake | Milwaukee | C | Metals (other than mercury), Pathogens (E. coli, fecal), PCBs | ✓ |
| Lower Turtle Lake | Barron | C | Nutrients (phosphorus, nitrogen) | — |
| Otter Lake | Vilas | C | Nutrients (phosphorus, nitrogen) | — |
| Lower Spring Lake | Jefferson | C | Nutrients (phosphorus, nitrogen) | — |
| Lost Lake | Vilas | C | Cause unknown | — |
| Harpt Lake | Manitowoc | C | Nutrients (phosphorus, nitrogen) | ✓ |
| North White Ash Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Scattering Rice Lake | Vilas | C | Cause unknown | — |
| Mauthe Lake | Fond du Lac | C | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Wapogasset Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Camelia Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Little Trade Lake | Burnett | C | Nutrients (phosphorus, nitrogen) | — |
| Schoenick Lake at | Shawano | C | Nutrients (phosphorus, nitrogen) | — |
| Lake Wingra | Dane | C | PCBs | — |
| Bakkens Pond | Sauk | C | Nutrients (phosphorus, nitrogen) | — |
| Little Arbor Vitae Lake | Vilas | C | Nutrients (phosphorus, nitrogen) | — |
| Lake Mendota | Dane | C | Nutrients (phosphorus, nitrogen) | ✓ |
| Little Blake Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Magnor Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Little Bass Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Unnamed Rusk Co -Deep Hole Lake | Rusk | C | Mercury | — |
| Alexander Lake | Lincoln | C | Cause unknown | — |
| Hill Slough Lake | Sauk | C | Nutrients (phosphorus, nitrogen) | — |
| Mirror Lake | Sauk | D | Nutrients (phosphorus, nitrogen) | — |
| Bass Lake | Burnett | D | Nutrients (phosphorus, nitrogen) | — |
| Indian Lake | Langlade | D | Mercury | — |
| Planting Ground Lake | Oneida | D | Mercury | — |
| Lake Montanis | Barron | D | Nutrients (phosphorus, nitrogen) | — |
| Mccann Lake | Rusk | D | Nutrients (phosphorus, nitrogen) | — |
| Clear Lake | Rock | D | Cause unknown | — |
| Rice Lake | Walworth | D | Nutrients (phosphorus, nitrogen) | — |
| Little Butternut Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Pike Lake | Price | D | Nutrients (phosphorus, nitrogen) | — |
| Turner Lake | Price | D | Nutrients (phosphorus, nitrogen) | — |
| Moen Lake | Oneida | D | Mercury | — |
| Duck Lake | Vilas | D | Nutrients (phosphorus, nitrogen) | — |
| Eagle Lake | Vilas | D | Cause unknown | — |
| Mud Lake | Washburn | D | Nutrients (phosphorus, nitrogen) | — |
| Boot Lake | Vilas | D | Cause unknown | — |
| Solberg Lake | Price | D | Mercury | — |
| Emma Lake | Oneida | D | Mercury | — |
| Hat Rapids Flowage Lake | Oneida | D | Mercury | — |
| Milwaukee Harbor South Half Lake | Milwaukee | D | Metals (other than mercury), Pathogens (E. coli, fecal), PCBs | ✓ |
| Lac Sault Dore Lake | Price | D | Nutrients (phosphorus, nitrogen) | — |
| Second Lake | Oneida | D | Mercury | — |
| Lake Mallalieu | St. Croix | D | Nutrients (phosphorus, nitrogen) | — |
| Milwaukee Harbor Lake | Milwaukee | D | Metals (other than mercury), Pathogens (E. coli, fecal), PCBs | ✓ |
| Crystal Lake | Oneida | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Waubesa | Dane | D | Nutrients (phosphorus, nitrogen), PFAS | ✓ |
| Deep Hole Lake | Langlade | D | Nutrients (phosphorus, nitrogen) | — |
| Yellow Birch Lake | Vilas | D | Nutrients (phosphorus, nitrogen) | — |
| Third Lake | Oneida | D | Mercury | — |
| Upper Park Falls Flowage Lake | Price | D | Mercury, Metals (other than mercury) | — |
| Tug Lake | Lincoln | D | Mercury | — |
| Bullhead Lake | Manitowoc | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Lynx Lake | Vilas | D | Nutrients (phosphorus, nitrogen) | — |
| Big Butternut Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Gass Lake | Manitowoc | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Vincent Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Pelican Lake | Oneida | D | Cause unknown | — |
| Spirit River Flowage Lake | Lincoln | D | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Old Taylor Lake | Waupaca | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Amik Lake | Vilas | D | Nutrients (phosphorus, nitrogen) | — |
| Deep Hole Lake | Langlade | D | Nutrients (phosphorus, nitrogen) | — |
| Horse Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Milwaukee Harbor Estuary Lake | Milwaukee | D | Metals (other than mercury), Pathogens (E. coli, fecal), PCBs | ✓ |
| Granite Lake South Basin | Barron | D | Cause unknown | — |
| Dowling Lake | Douglas | D | Cause unknown | — |
| Wilson Flowage Lake | Price | D | Nutrients (phosphorus, nitrogen) | — |
| Deep Hole Lake | Langlade | D | Nutrients (phosphorus, nitrogen) | — |
| Clam Lake | Burnett | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Shangrila -Benet | Kenosha | D | Nutrients (phosphorus, nitrogen) | — |
| Moon Bay Lake | Chippewa | D | Nutrients (phosphorus, nitrogen) | — |
| Caldron Falls Reservoir | Marinette | D | Mercury | — |
| Dunn Lake | Vilas | D | Cause unknown | — |
| Largon Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Wissota | Chippewa | D | Nutrients (phosphorus, nitrogen), PCBs | — |
| Lake Monona | Dane | D | Nutrients (phosphorus, nitrogen), PFAS, PCBs | ✓ |
| Hallie Lake | Chippewa | D | Turbidity | — |
| Apple River Flowage Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Ne Bay Lake | Vilas | D | Cause unknown | — |
| Turtle-Flambeau Flowage Lake | Iron | D | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Swan Lake | Columbia | D | Cause unknown | ✓ |
| Seneca Lake | Vilas | D | Nutrients (phosphorus, nitrogen) | — |
| Lac la Belle Lake | Waukesha | D | Nutrients (phosphorus, nitrogen), PCBs | — |
| Sheas Lake | Kewaunee | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Omer Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Madeline Lake | Oneida | D | Mercury | — |
| Big Doctor Lake | Burnett | D | Nutrients (phosphorus, nitrogen) | — |
| Big Round Deep Hole South Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Catfish Lake | Vilas | D | Cause unknown | — |
| Kettle Lake | Langlade | D | Mercury | — |
| Pokegama Lake | Barron | D | Nutrients (phosphorus, nitrogen) | — |
| Bittersweet Lake | Vilas | D | Nutrients (phosphorus, nitrogen) | — |
| Duluth Lake | Douglas | D | Metals (other than mercury), Other cause, Toxic organics | — |
| Big Blake Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Blockhouse Lake | Price | D | Nutrients (phosphorus, nitrogen) | — |
| Birch Lake | Sawyer | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Chetac | Sawyer | D | Nutrients (phosphorus, nitrogen) | — |
| Park Lake | Columbia | D | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Lake of the Woods Barron Co. at | Barron | D | Nutrients (phosphorus, nitrogen) | — |
| Long Trade Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Tainter Lake | Dunn | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Mud Lake | Jefferson | D | Nutrients (phosphorus, nitrogen) | — |
| Mud Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Petenwell Flowage Lake | Juneau | D | Dioxins, Mercury, Nutrients (phosphorus, nitrogen) +2 more | ✓ |
| Peterson Lake | Oconto | D | Nutrients (phosphorus, nitrogen) | — |
| Apple Lake | St. Croix | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Hoerth Lake | Oconto | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Dubay | Marathon | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Spring Lake | Columbia | D | Nutrients (phosphorus, nitrogen) | — |
| Leota Lake | Rock | D | Nutrients (phosphorus, nitrogen) | — |
| Spirit Lake | Taylor | D | Nutrients (phosphorus, nitrogen) | — |
| White Ash Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Weyers Lake | Manitowoc | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Carstens Lake | Manitowoc | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Lazy Lake | Columbia | D | Nutrients (phosphorus, nitrogen) | — |
| Musser Lake | Price | D | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Pella Lake | Shawano | D | Cause unknown | — |
| Alabama Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Eau Claire Lake | Eau Claire | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Menomin | Dunn | D | Nutrients (phosphorus, nitrogen) | ✓ |
| St. Louis River Outlet Upstream of John A. Blatnik Memorial Bridge Lake | Douglas | D | Mercury, Metals (other than mercury), PCBs | — |
| Lake Redstone | Sauk | F | Nutrients (phosphorus, nitrogen) | ✓ |
| Silver Lake | Manitowoc | F | Nutrients (phosphorus, nitrogen) | ✓ |
| Prairie Lake | Barron | F | Nutrients (phosphorus, nitrogen) | — |
| Indian Lake | Dane | F | Nutrients (phosphorus, nitrogen) | — |
| Big Eau Pleine Lake | Marathon | F | Nutrients (phosphorus, nitrogen) | ✓ |
| East Bay Lake | Vilas | F | Cause unknown | — |
| Cranberry Lake | Taylor | F | Nutrients (phosphorus, nitrogen) | — |
| Beaver Dam Lake | Dodge | F | Nutrients (phosphorus, nitrogen) | ✓ |
| Long Lake | Manitowoc | F | Nutrients (phosphorus, nitrogen) | ✓ |
| Long Lake | Price | F | Nutrients (phosphorus, nitrogen) | — |
| Lake Winneconne | Winnebago | F | Cause unknown, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Lake Butte des Morts | Winnebago | F | Cause unknown, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Island Lake | Iron | F | Mercury | — |
| Altoona Lake | Eau Claire | F | Nutrients (phosphorus, nitrogen) | — |
| Eagle Lake | Racine | F | Nutrients (phosphorus, nitrogen) | — |
| Potato Lake | Rusk | F | Nutrients (phosphorus, nitrogen) | — |
| Mud Lake | Polk | F | Nutrients (phosphorus, nitrogen) | — |
| Mud Lake | Barron | F | Nutrients (phosphorus, nitrogen) | — |
| Comus Lake | Walworth | F | Nutrients (phosphorus, nitrogen) | — |
| Fox Lake | Dodge | F | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Lake Poygan | Winnebago | F | Cause unknown, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Crowley Flowage Lake | Price | F | Mercury | — |
| Dynamite Lake | Langlade | F | Nutrients (phosphorus, nitrogen) | — |
| Lake Koshkonong | Jefferson | F | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Lower Park Falls Flowage Lake | Price | F | Mercury, Metals (other than mercury) | — |
| Ludden Lake | Iowa | F | Nutrients (phosphorus, nitrogen) | — |
| Tenmile Lake | Barron | F | Nutrients (phosphorus, nitrogen) | — |
| Beckers Lake | Calumet | F | Nutrients (phosphorus, nitrogen) | ✓ |
| Upper Kelly Lake | Waukesha | F | Nutrients (phosphorus, nitrogen) | — |
| Staples Lake | Barron | F | Nutrients (phosphorus, nitrogen) | — |
| West Bay Lake | Vilas | F | Cause unknown | — |
| Mason Lake | Adams | F | Nutrients (phosphorus, nitrogen) | ✓ |
| Lake Wisconsin Columbia Co. | Columbia | F | Mercury, Nutrients (phosphorus, nitrogen), PCBs | ✓ |
| Buffalo Lake | Marquette | F | PCBs | — |
| Tiedman Pond | Dane | F | Nutrients (phosphorus, nitrogen) | — |
| Klaus Lake | Oconto | F | Nutrients (phosphorus, nitrogen) | — |
| Clam River Flowage Lake | Burnett | F | Nutrients (phosphorus, nitrogen) | — |
| Pixley Flowage Lake | Price | F | Mercury | — |
| Upper Vermillion Lake | Barron | F | Nutrients (phosphorus, nitrogen) | — |
| Chequamegon Waters Flowage Lake | Taylor | F | Nutrients (phosphorus, nitrogen) | — |
| Odana Pond | Dane | F | Nutrients (phosphorus, nitrogen), Salinity / chlorides | — |
| Little Green Lake | Green Lake | F | Nutrients (phosphorus, nitrogen) | ✓ |
| Lotus Lake | Polk | F | Nutrients (phosphorus, nitrogen) | — |
| Prairie Lake | Barron | F | Nutrients (phosphorus, nitrogen) | — |
| Yellowstone Lake | Lafayette | F | Nutrients (phosphorus, nitrogen) | — |
| Mead Lake | Clark | F | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Lake Delton | Sauk | F | Nutrients (phosphorus, nitrogen) | ✓ |
| Lake Shangri-la | Kenosha | F | Nutrients (phosphorus, nitrogen) | — |
| Lake Wisconsin Palisade Street Bay | Sauk | F | Mercury, Nutrients (phosphorus, nitrogen), PCBs | ✓ |
| North Bay Lake | Vilas | F | Cause unknown | — |
| Neshonoc Lake | La Crosse | F | Mercury, Nutrients (phosphorus, nitrogen), Turbidity | — |
| Prairie Lake | Barron | F | Nutrients (phosphorus, nitrogen) | — |
| Little Twin Lake | Green Lake | F | Nutrients (phosphorus, nitrogen) | — |
| Upper Clam Lake | Burnett | F | Nutrients (phosphorus, nitrogen) | — |
| Pepin Lake | Pepin | F | Nutrients (phosphorus, nitrogen) | — |
| Carrol Lake | Oneida | F | Nutrients (phosphorus, nitrogen) | — |
| Mead Lake Nb Test Site | Clark | F | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Mead Lake Nb Control Site | Clark | F | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Dexter Lake | Wood | F | Nutrients (phosphorus, nitrogen), Pathogens (E. coli, fecal) | — |
| Lake Tomah | Monroe | F | Nutrients (phosphorus, nitrogen) | — |
| Little Yellow Lake | Burnett | F | Nutrients (phosphorus, nitrogen) | — |
| Silver Creek Estuary Lake | Green Lake | F | Pathogens (E. coli, fecal) | — |
| Graber Pond | Dane | F | Nutrients (phosphorus, nitrogen) | — |
| Lower Kelly Lake | Waukesha | F | Nutrients (phosphorus, nitrogen) | — |
Frequently Asked Questions
How many lakes are impaired in Wisconsin?
518 of 1,422 graded Wisconsin lakes (36%) are listed as impaired in the most recent EPA ATTAINS reporting cycle. Of those, 463 are on the federal Clean Water Act §303(d) list and 77 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) (296 lakes); Mercury (134 lakes); Cause unknown (89 lakes); PCBs (26 lakes); Metals (other than mercury) (17 lakes); Turbidity (15 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.