Impaired Lakes in Wisconsin
473 of 1,353 graded Wisconsin lakes (35%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 61 have an approved TMDL restoration plan.
Top Causes of Impairment in Wisconsin
269
Nutrients (phosphorus, nitrogen)
129
Mercury
82
Cause unknown
15
PCBs
13
Turbidity
8
Metals (other than mercury)
6
PFAS
5
Pathogens (E. coli, fecal)
Reading the Wisconsin impairment landscape
Wisconsin reports 473 impaired lakes — 35% of the state's 1,353 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 473 EPA-Listed Impaired Lakes in Wisconsin
| Lake | County | Grade | Causes | TMDL |
|---|---|---|---|---|
| Green Lake | Green Lake | A | Nutrients (phosphorus, nitrogen) | ✓ |
| Lake Beulah | Walworth | A | Nutrients (phosphorus, nitrogen) | — |
| Lac Courte Oreilles Lake | Sawyer | A | Cause unknown | — |
| Whitefish Lake | Sawyer | A | Mercury | — |
| Sand Lake | Barron | A | Cause unknown | — |
| Sand Lake | Sawyer | A | Mercury | — |
| Durphee Lake | Sawyer | A | Cause unknown | — |
| Wind Lake | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Potter Lake | Walworth | B | Nutrients (phosphorus, nitrogen) | — |
| Lake St Croix | St. Croix | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Spider Lake | Iron | B | Mercury | — |
| Spider Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Pickerel Lake | Forest | B | Cause unknown | — |
| Pickerel Lake | Vilas | B | Cause unknown | — |
| Pickerel Lake | Lincoln | B | Mercury | — |
| North Turtle Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Balsam Lake | Washburn | B | Nutrients (phosphorus, nitrogen) | — |
| Silver Lake | Barron | B | Mercury | — |
| Silver Lake | Vilas | B | Cause unknown | — |
| Whitefish Lake | Oneida | B | Mercury | — |
| Round Lake | Shawano | B | Cause unknown | ✓ |
| Round Lake | Chippewa | B | Mercury | — |
| Round Lake | Oneida | B | Mercury | — |
| Cedar Lake | Iron | B | Mercury | — |
| Mirror Lake | Waupaca | B | Cause unknown | — |
| Deep Lake | Washburn | B | Nutrients (phosphorus, nitrogen) | — |
| Beasley Lake | Waupaca | B | Nutrients (phosphorus, nitrogen) | — |
| Bass Lake | Price | B | Mercury | — |
| Bass Lake | Barron | B | Nutrients (phosphorus, nitrogen) | — |
| Bass Lake | Vilas | B | Cause unknown | — |
| Bass Lake | Lincoln | B | Mercury | — |
| Little Friess Lake | Washington | B | Cause unknown | — |
| Clear Lake | Rusk | B | Nutrients (phosphorus, nitrogen) | — |
| Clear Lake | Oneida | B | Mercury | — |
| Pioneer Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Sugar Camp Lake | Oneida | B | Mercury | — |
| Bone Lake | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Marl Lake | Waupaca | B | Nutrients (phosphorus, nitrogen) | — |
| Indian Lake | Oneida | B | Mercury | — |
| Turtle Flambeau Flowage Lake | Iron | B | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Oxbow Lake | Vilas | B | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Bear Lake | Forest | B | Cause unknown | — |
| Bear Lake | Barron | B | Nutrients (phosphorus, nitrogen) | — |
| Long Lake | Washburn | B | Nutrients (phosphorus, nitrogen) | — |
| Long Lake | Waupaca | B | Nutrients (phosphorus, nitrogen) | — |
| Long Lake | Shawano | B | Cause unknown | ✓ |
| Long Lake | Lincoln | B | Mercury | — |
| Nelson Lake | Sawyer | B | Nutrients (phosphorus, nitrogen) | — |
| North Lake | Waukesha | B | Nutrients (phosphorus, nitrogen) | — |
| Crescent Lake | Oneida | B | Mercury | — |
| Crescent Lake | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Red Cedar Lake | Barron | B | Nutrients (phosphorus, nitrogen) | — |
| Shadow Lake | Waupaca | B | Cause unknown | — |
| Pipe Lake | Polk | B | Mercury | — |
| Rainbow Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Camelot Lake | Adams | B | Cause unknown | — |
| Grass Lake | Shawano | B | Cause unknown | ✓ |
| Island Lake | Oneida | B | Mercury | — |
| Saint Croix Flowage Lake | Douglas | B | Mercury | — |
| Mud Lake | Polk | B | Cause unknown | — |
| Big Lake | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Lac la Belle Lake | Waukesha | B | Nutrients (phosphorus, nitrogen), PCBs | — |
| Big Arbor Vitae Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Little Sand Lake | Forest | B | Mercury | — |
| Bearskin Lake | Oneida | B | Cause unknown | — |
| Mid Lake | Oneida | B | Mercury | — |
| Hartlaub Lake | Manitowoc | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Mcdonald Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Little Pine Lake | Iron | B | Mercury | — |
| Bahr Lake | Shawano | B | Cause unknown | — |
| Lake Esadore | Taylor | B | Mercury | — |
| Amnicon Lake | Douglas | B | Cause unknown, Turbidity | — |
| Armour Lake | Vilas | B | Mercury | — |
| Big Dummy Lake | Barron | B | Nutrients (phosphorus, nitrogen) | — |
| Found Lake | Vilas | B | Cause unknown | — |
| Ward Lake | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Crane Lake | Forest | B | Cause unknown | — |
| Diamond Lake | Bayfield | B | Mercury | — |
| Alva Lake | Oneida | B | Mercury | — |
| Franklin Lake | Oneida | B | Mercury | — |
| Church Pine Lake | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Whitewater Lake | Walworth | B | Nutrients (phosphorus, nitrogen) | — |
| Echo Lake | Barron | B | Cause unknown | — |
| Tahkodah Lake | Bayfield | B | Mercury | — |
| Annabelle Lake | Vilas | B | Mercury | — |
| Crystal Lake | Sheboygan | B | Mercury | — |
| Lower Vermillion Lake | Barron | B | Cause unknown | — |
| Perch Lake | Oneida | B | Mercury | — |
| Lake Waubesa | Dane | B | Nutrients (phosphorus, nitrogen), PFAS | ✓ |
| Meta Lake | Vilas | B | Cause unknown | — |
| Forest Lake | Fond du Lac | B | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Turtle Lake | Walworth | B | Cause unknown | — |
| Friess Lake | Washington | B | Nutrients (phosphorus, nitrogen) | — |
| Wood Lake | Burnett | B | Nutrients (phosphorus, nitrogen) | — |
| Horseshoe Lake | Polk | B | Cause unknown | — |
| Horseshoe Lake | Manitowoc | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Paddock Lake | Kenosha | B | Nutrients (phosphorus, nitrogen) | — |
| Auburn Lake | Fond du Lac | B | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Sunset Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Schnur Lake | Price | B | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Horsehead Lake | Vilas | B | Mercury, Nutrients (phosphorus, nitrogen) | — |
| St Croix Flowage Lake | Douglas | B | Mercury | — |
| Maple Lake | Oneida | B | Mercury | — |
| Windigo Lake | Sawyer | B | Mercury | — |
| Korth Lake | Shawano | B | Cause unknown | — |
| Ballard Lake | Vilas | B | Mercury | — |
| Lynx Lake | Vilas | B | Mercury | — |
| Beaver Lake | Vilas | B | Cause unknown | — |
| Seven Island Lake | Lincoln | B | Mercury | — |
| Big Stone Lake | Oneida | B | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Snipe Lake | Vilas | B | Mercury | — |
| Pine Lake | Iron | B | Mercury | — |
| Pine Lake | Shawano | B | Cause unknown | ✓ |
| Moon Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Lipsett Lake | Burnett | B | Cause unknown | — |
| Lake Minnesuing | Douglas | B | Mercury | — |
| Lake Sherwood | Adams | B | Cause unknown | — |
| Spirit Lake | Oneida | B | Mercury | — |
| Fowler Lake | Waukesha | B | Nutrients (phosphorus, nitrogen), PCBs | — |
| Youngs Lake Waupaca Co | Waupaca | B | Nutrients (phosphorus, nitrogen) | — |
| Virgin Lake | Oneida | B | Mercury | — |
| Lake Nebagamon | Douglas | B | Mercury | — |
| Otter Lake | Waupaca | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Big Bass Lake | Marathon | B | Mercury | — |
| Big Moon Lake at | Barron | B | Nutrients (phosphorus, nitrogen) | — |
| Columbia Lake | Waupaca | B | Nutrients (phosphorus, nitrogen) | — |
| Gilmore Lake | Washburn | B | Nutrients (phosphorus, nitrogen) | — |
| English Lake | Manitowoc | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Elkhart Lake | Sheboygan | B | Mercury | — |
| Arrowhead Lake | Adams | B | Cause unknown | — |
| Lake Julia | Oneida | B | Mercury | — |
| 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 | — |
| Collins Lake | Portage | B | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Granite Lake at | Barron | B | Cause unknown | — |
| Lower Phantom Lake | Waukesha | B | Nutrients (phosphorus, nitrogen) | — |
| Alma Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Axhandle Lake | Chippewa | B | Mercury | — |
| Irving Lake | Vilas | B | Mercury | — |
| Tuma Lake | Manitowoc | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Tichigan Lake | Racine | B | PCBs | — |
| Lake Pesobic | Lincoln | B | Mercury | — |
| Finger Lake | Vilas | B | Cause unknown | — |
| Red Bass Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Lake Wingra | Dane | B | PCBs | — |
| Antler Lake | Polk | B | Nutrients (phosphorus, nitrogen) | — |
| Williams Lake | Marquette | B | PCBs | — |
| Mccullough Lake | Vilas | B | Cause unknown | — |
| Bakkens Pond | Sauk | B | Nutrients (phosphorus, nitrogen) | — |
| Hunter Lake | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Lone Stone Lake | Oneida | B | Mercury | — |
| Oneida Lake | Oneida | B | Cause unknown | — |
| Little Bearskin Lake | Oneida | B | Cause unknown | — |
| Big Mckenzie Lake | Washburn | B | Nutrients (phosphorus, nitrogen) | — |
| De Neveu Lake | Fond du Lac | B | Nutrients (phosphorus, nitrogen) | — |
| Upper Gresham Lake | Vilas | B | Mercury | — |
| Kasbaum Lake | Manitowoc | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Moccasin Lake | Oneida | B | Mercury | — |
| Pope Lake | Waupaca | B | Nutrients (phosphorus, nitrogen) | — |
| Army Lake | Walworth | B | Nutrients (phosphorus, nitrogen) | — |
| Middle Mckenzie Lake | Burnett | B | Nutrients (phosphorus, nitrogen) | — |
| Little Dummy Lake | Barron | B | Nutrients (phosphorus, nitrogen) | — |
| Little Cedar Lake | Washington | B | Cause unknown | — |
| Arbutus Lake | Forest | B | Cause unknown | — |
| Lake Content | Vilas | B | Nutrients (phosphorus, nitrogen) | — |
| Cross Lake | Kenosha | B | Nutrients (phosphorus, nitrogen) | — |
| Lake Buteau | Lincoln | B | Mercury | — |
| Little Fork Lake | Oneida | B | Mercury | — |
| Slim Lake | Washburn | B | Nutrients (phosphorus, nitrogen) | — |
| Ocauchee Lake | Waukesha | B | Nutrients (phosphorus, nitrogen) | — |
| Okauchee Lake Site | Waukesha | B | Nutrients (phosphorus, nitrogen) | — |
| Taylor Lake | Waupaca | B | Nutrients (phosphorus, nitrogen) | ✓ |
| Oneonta Lake | Marinette | B | Cause unknown | — |
| Siskiwit Lake | Bayfield | B | Mercury | — |
| Day Lake | Vilas | B | Mercury | — |
| Dace Lake | Polk | B | Cause unknown | — |
| Delavan Lake | Walworth | C | Nutrients (phosphorus, nitrogen) | — |
| Cranberry Lake | Oneida | C | Cause unknown | — |
| Round Lake | Price | C | Nutrients (phosphorus, nitrogen) | — |
| Clear Lake | Rock | C | Cause unknown | — |
| Rice Lake | Barron | C | Nutrients (phosphorus, nitrogen) | — |
| Rice Lake | Vilas | C | Nutrients (phosphorus, nitrogen) | — |
| Townline Lake | Oneida | C | Mercury | — |
| Long Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Long Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Birch Lake | Washburn | C | Nutrients (phosphorus, nitrogen) | — |
| Dog Lake | Oneida | C | Mercury | — |
| Lake Alice | Lincoln | C | Oxygen depletion (low DO) | — |
| Rock Lake | Vilas | C | Nutrients (phosphorus, nitrogen) | — |
| Pike Lake | Price | C | Nutrients (phosphorus, nitrogen) | — |
| Turner Lake | Price | C | Nutrients (phosphorus, nitrogen) | — |
| Big Round Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Butternut Lake | Price | C | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Moen Lake | Oneida | C | Mercury | — |
| Lake Emily | Dodge | C | Nutrients (phosphorus, nitrogen) | ✓ |
| Deer Lake | Oneida | C | Mercury | — |
| Duck Lake | Langlade | C | Nutrients (phosphorus, nitrogen) | — |
| Loon Lake | Chippewa | C | Mercury | — |
| Little Sand Lake | Barron | C | Cause unknown | — |
| Stella Lake | Vilas | C | Mercury | — |
| Lake Mohawksin | Lincoln | C | Oxygen depletion (low DO), PFAS | — |
| Solberg Lake | Price | C | Mercury | — |
| Milwaukee River Lake | Milwaukee | C | Metals (other than mercury), Pathogens (E. coli, fecal), PCBs | ✓ |
| Laurel Lake | Oneida | C | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Fourmile Lake | Oneida | C | Mercury | — |
| White Clay Lake | Shawano | C | Nutrients (phosphorus, nitrogen) | ✓ |
| Big Trade Lake | Burnett | C | Nutrients (phosphorus, nitrogen) | — |
| Hancock Lake | Oneida | C | Cause unknown | — |
| Spring Lake | Portage | C | Nutrients (phosphorus, nitrogen) | ✓ |
| White Mound Lake | Sauk | C | Cause unknown | — |
| Shawano Lake | Shawano | C | Nutrients (phosphorus, nitrogen) | ✓ |
| Tug Lake | Lincoln | C | Mercury | — |
| Upper Turtle Lake | Barron | C | Nutrients (phosphorus, nitrogen) | — |
| North Spirit Lake | Price | C | Cause unknown | — |
| Pine Lake | Forest | C | Cause unknown | — |
| Moon Lake | Barron | C | Nutrients (phosphorus, nitrogen) | — |
| Moose Lake | Sawyer | C | Mercury | — |
| Loveless Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Muskellunge Lake | Vilas | C | Cause unknown | — |
| Amik Lake | Vilas | 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) | ✓ |
| Amacoy Lake | Rusk | C | Cause unknown | — |
| North Pipe Lake | Polk | C | Cause unknown | — |
| Scattering Rice Lake | Vilas | C | Cause unknown | — |
| Enterprise Lake | Langlade | C | Cause unknown | — |
| Bear Trap Lake | Polk | C | Cause unknown | — |
| Yellow Lake | Burnett | C | Nutrients (phosphorus, nitrogen) | — |
| Mauthe Lake | Fond du Lac | C | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Wapogasset Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Camelia Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Lake Shangrila -Benet | Kenosha | C | Nutrients (phosphorus, nitrogen) | — |
| Little Arbor Vitae Lake | Vilas | C | Nutrients (phosphorus, nitrogen) | — |
| Mckenzie Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Mineral Lake | Ashland | C | Nutrients (phosphorus, nitrogen) | — |
| Poskin Lake | Barron | C | Nutrients (phosphorus, nitrogen) | — |
| Little Bass Lake | Polk | C | Nutrients (phosphorus, nitrogen) | — |
| Lake Lorraine | Walworth | C | Nutrients (phosphorus, nitrogen) | — |
| East Wetland Inlet To Lake Ree | Bayfield | C | Mercury | — |
| Lake Montanis | Barron | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Redstone | Sauk | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Beaver Dam Lake | Dodge | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Round Lake | Burnett | D | Nutrients (phosphorus, nitrogen) | — |
| Cedar Lake | Polk | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Mirror Lake | Sauk | D | Nutrients (phosphorus, nitrogen) | — |
| Tainter Lake | Dunn | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Rice Lake | Walworth | D | Nutrients (phosphorus, nitrogen) | — |
| Long Trade Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Indian Lake | Dane | D | Nutrients (phosphorus, nitrogen) | — |
| Hidden Valley Lake | Lafayette | D | Nutrients (phosphorus, nitrogen) | — |
| Big Eau Pleine Lake | Marathon | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Long Lake | Manitowoc | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Lake Puckaway | Green Lake | D | Cause unknown, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Mud Lake | Jefferson | D | Nutrients (phosphorus, nitrogen) | — |
| Mud Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Mud Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Altoona Lake | Eau Claire | D | Nutrients (phosphorus, nitrogen) | — |
| Eagle Lake | Racine | D | Nutrients (phosphorus, nitrogen) | — |
| Comus Lake | Walworth | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Desair | Barron | D | Nutrients (phosphorus, nitrogen), Turbidity | — |
| Fox Lake | Dodge | D | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Porcupine Lake-Deep Hole | Oconto | D | Nutrients (phosphorus, nitrogen) | — |
| Petenwell Flowage Lake | Juneau | D | Dioxins, Mercury, Nutrients (phosphorus, nitrogen) +2 more | ✓ |
| Lake Kegonsa | Dane | D | Nutrients (phosphorus, nitrogen), PFAS | ✓ |
| Crystal Lake | Oneida | D | Nutrients (phosphorus, nitrogen) | — |
| Apple Lake | St. Croix | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Lac Sault Dore Lake | Price | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Mallalieu | St. Croix | D | Nutrients (phosphorus, nitrogen) | — |
| Peterson Lake | Oconto | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Koshkonong | Jefferson | D | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Holcombe Flowage Lake | Chippewa | D | Nutrients (phosphorus, nitrogen), Turbidity | — |
| Ludden Lake | Iowa | D | Nutrients (phosphorus, nitrogen) | — |
| Hoerth Lake | Oconto | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Dubay | Marathon | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Beckers Lake | Calumet | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Spring Lake | Columbia | D | Nutrients (phosphorus, nitrogen) | — |
| Staples Lake | Barron | D | Nutrients (phosphorus, nitrogen) | — |
| Bullhead Lake | Manitowoc | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Leota Lake | Rock | D | Nutrients (phosphorus, nitrogen) | — |
| Big Butternut Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Gass Lake | Manitowoc | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Spirit Lake | Taylor | D | Nutrients (phosphorus, nitrogen) | — |
| Spirit River Flowage Lake | Lincoln | D | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Lower Turtle Lake | Barron | D | Nutrients (phosphorus, nitrogen) | — |
| White Ash Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Mason Lake | Adams | D | Nutrients (phosphorus, nitrogen) | ✓ |
| North White Ash Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Buffalo Lake | Marquette | D | PCBs | — |
| Dowling Lake | Douglas | D | Cause unknown | — |
| Klaus Lake | Oconto | D | Nutrients (phosphorus, nitrogen) | — |
| Wilson Flowage Lake | Price | D | Nutrients (phosphorus, nitrogen) | — |
| Clam Lake | Burnett | D | Nutrients (phosphorus, nitrogen) | — |
| Little Trade Lake | Burnett | D | Nutrients (phosphorus, nitrogen) | — |
| Upper Vermillion Lake | Barron | D | Nutrients (phosphorus, nitrogen) | — |
| Weyers Lake | Manitowoc | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Carstens Lake | Manitowoc | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Chequamegon Waters Flowage Lake | Taylor | D | Nutrients (phosphorus, nitrogen) | — |
| Odana Pond | Dane | D | Nutrients (phosphorus, nitrogen), Salinity / chlorides | — |
| Little Green Lake | Green Lake | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Schoenick Lake at | Shawano | D | Nutrients (phosphorus, nitrogen) | — |
| Lazy Lake | Columbia | D | Nutrients (phosphorus, nitrogen) | — |
| Largon Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Wissota | Chippewa | D | Nutrients (phosphorus, nitrogen), PCBs | — |
| Easton Lake | Adams | D | Cause unknown | — |
| Lake Monona | Dane | D | Nutrients (phosphorus, nitrogen), PFAS, PCBs | ✓ |
| Yellowstone Lake | Lafayette | D | Nutrients (phosphorus, nitrogen) | — |
| Musser Lake | Price | D | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Apple River Flowage Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Mendota | Dane | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Alabama Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Little Blake Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Eau Claire Lake | Eau Claire | D | Nutrients (phosphorus, nitrogen) | — |
| Magnor Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Alexander Lake | Lincoln | D | Cause unknown | — |
| Lake Menomin | Dunn | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Omer Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Hill Slough Lake | Sauk | D | Nutrients (phosphorus, nitrogen) | — |
| Big Blake Lake | Polk | D | Nutrients (phosphorus, nitrogen) | — |
| Dexter Lake | Wood | D | Nutrients (phosphorus, nitrogen), Pathogens (E. coli, fecal) | — |
| Lake Chetac North Basin | Sawyer | D | Nutrients (phosphorus, nitrogen) | — |
| Birch Lake | Sawyer | D | Nutrients (phosphorus, nitrogen) | — |
| Lake Tomah | Monroe | D | Nutrients (phosphorus, nitrogen) | — |
| Silver Creek Estuary Lake | Green Lake | D | Pathogens (E. coli, fecal) | — |
| Pickerel Lake | Portage | NR | Nutrients (phosphorus, nitrogen) | — |
| East Bay Lake | Vilas | NR | Cause unknown | — |
| Cranberry Lake | Taylor | NR | Nutrients (phosphorus, nitrogen) | — |
| Silver Lake | Manitowoc | NR | Nutrients (phosphorus, nitrogen) | ✓ |
| Mccann Lake | Rusk | NR | Nutrients (phosphorus, nitrogen) | — |
| Prairie Lake | Barron | NR | Nutrients (phosphorus, nitrogen) | — |
| Round Lake | Waupaca | NR | Nutrients (phosphorus, nitrogen) | — |
| Round Lake | Polk | NR | Nutrients (phosphorus, nitrogen) | — |
| Bass Lake | Oneida | NR | Mercury | — |
| Bass Lake | Burnett | NR | Nutrients (phosphorus, nitrogen) | — |
| Indian Lake | Langlade | NR | Mercury | — |
| Indian Lake | Oneida | NR | Cause unknown | — |
| Little Butternut Lake | Polk | NR | Nutrients (phosphorus, nitrogen) | — |
| Planting Ground Lake | Oneida | NR | Mercury | — |
| Milwaukee Harbor Lake | Milwaukee | NR | Metals (other than mercury), Pathogens (E. coli, fecal), PCBs | ✓ |
| Chain Lake | Chippewa | NR | Mercury | — |
| Long Lake | Oneida | NR | Mercury | — |
| Long Lake | Price | NR | Nutrients (phosphorus, nitrogen) | — |
| Birch Lake | Oneida | NR | Cause unknown | — |
| Lakeshore State Park Fish Shocking | Milwaukee | NR | Metals (other than mercury), Pathogens (E. coli, fecal), PCBs | ✓ |
| Pike Lake | Polk | NR | Nutrients (phosphorus, nitrogen) | — |
| Lake Winneconne | Winnebago | NR | Cause unknown, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Lake Butte des Morts | Winnebago | NR | Cause unknown, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Wolf Lake | Portage | NR | Nutrients (phosphorus, nitrogen) | — |
| Cooley Lake | Oconto | NR | Nutrients (phosphorus, nitrogen) | — |
| Stone Lake | Vilas | NR | Nutrients (phosphorus, nitrogen) | — |
| Fawn Lake | Vilas | NR | Nutrients (phosphorus, nitrogen) | — |
| Potato Lake | Rusk | NR | Nutrients (phosphorus, nitrogen) | — |
| Hemlock Lake | Oneida | NR | Mercury | — |
| Island Lake | Vilas | NR | Nutrients (phosphorus, nitrogen) | — |
| Island Lake | Iron | NR | Mercury | — |
| Mud Lake | Barron | NR | Nutrients (phosphorus, nitrogen) | — |
| Mud Lake | Washburn | NR | Nutrients (phosphorus, nitrogen) | — |
| Duck Lake | Vilas | NR | Nutrients (phosphorus, nitrogen) | — |
| Boot Lake | Vilas | NR | Cause unknown | — |
| Eagle Lake | Vilas | NR | Cause unknown | — |
| White Lake | Oconto | NR | Nutrients (phosphorus, nitrogen) | — |
| Walsh Lake | Forest | NR | Mercury | — |
| Hat Rapids Flowage Lake | Oneida | NR | Mercury | — |
| Emma Lake | Oneida | NR | Mercury | — |
| Sand Lake | Rusk | NR | Mercury | — |
| Sand Lake | Iron | NR | Mercury | — |
| Sand Lake | Florence | NR | Mercury | — |
| Crowley Flowage Lake | Price | NR | Mercury | — |
| Dynamite Lake | Langlade | NR | Nutrients (phosphorus, nitrogen) | — |
| Lake Poygan | Winnebago | NR | Cause unknown, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Crystal Lake | Bayfield | NR | Mercury | — |
| Second Lake | Oneida | NR | Mercury | — |
| West Horsehead Lake | Oneida | NR | Mercury | — |
| Deep Hole Lake | Langlade | NR | Nutrients (phosphorus, nitrogen) | — |
| White Birch Lake | Vilas | NR | Mercury | — |
| Yellow Birch Lake | Vilas | NR | Nutrients (phosphorus, nitrogen) | — |
| Lower Park Falls Flowage Lake | Price | NR | Mercury, Metals (other than mercury) | — |
| Tenmile Lake | Barron | NR | Nutrients (phosphorus, nitrogen) | — |
| Third Lake | Oneida | NR | Mercury | — |
| Upper Park Falls Flowage Lake | Price | NR | Mercury, Metals (other than mercury) | — |
| Upper Kelly Lake | Waukesha | NR | Nutrients (phosphorus, nitrogen) | — |
| Lynx Lake | Vilas | NR | Nutrients (phosphorus, nitrogen) | — |
| Bullhead Lake | Langlade | NR | Nutrients (phosphorus, nitrogen) | — |
| Beaver Lake | Chippewa | NR | Nutrients (phosphorus, nitrogen) | — |
| Robinson Pond | Jackson | NR | Mercury | — |
| Vincent Lake | Polk | NR | Nutrients (phosphorus, nitrogen) | — |
| Moose Lake | Waukesha | NR | Nutrients (phosphorus, nitrogen) | — |
| West Bay Lake | Vilas | NR | Cause unknown | — |
| Mary Lake | Lincoln | NR | Mercury | — |
| Pensaukee Lake | Shawano | NR | Nutrients (phosphorus, nitrogen) | ✓ |
| Pelican Lake | Oneida | NR | Cause unknown | — |
| Old Taylor Lake | Waupaca | NR | Nutrients (phosphorus, nitrogen) | ✓ |
| Deep Hole Lake | Langlade | NR | Nutrients (phosphorus, nitrogen) | — |
| Dorothy Lake | Oneida | NR | Mercury | — |
| Horse Lake | Polk | NR | Nutrients (phosphorus, nitrogen) | — |
| Porcupine Lake | Oconto | NR | Nutrients (phosphorus, nitrogen) | — |
| Bird Lake | Oneida | NR | Mercury | — |
| Buffalo Lake | Oneida | NR | Nutrients (phosphorus, nitrogen) | — |
| Tiedman Pond | Dane | NR | Nutrients (phosphorus, nitrogen) | — |
| Hill Lake | Oneida | NR | Nutrients (phosphorus, nitrogen) | ✓ |
| Deep Hole Lake | Langlade | NR | Nutrients (phosphorus, nitrogen) | — |
| Freedom Lakes | Polk | NR | Nutrients (phosphorus, nitrogen) | — |
| Clam River Flowage Lake | Burnett | NR | Nutrients (phosphorus, nitrogen) | — |
| Pixley Flowage Lake | Price | NR | Mercury | — |
| Lamont Lake | Polk | NR | Nutrients (phosphorus, nitrogen) | — |
| Big Twin Lake | Green Lake | NR | Nutrients (phosphorus, nitrogen) | ✓ |
| Moon Bay Lake | Chippewa | NR | Nutrients (phosphorus, nitrogen) | — |
| Caldron Falls Reservoir | Marinette | NR | Mercury | — |
| Lotus Lake | Polk | NR | Nutrients (phosphorus, nitrogen) | — |
| Shannon Lake | Vilas | NR | Mercury | — |
| Dunn Lake | Vilas | NR | Cause unknown | — |
| Dads Lake | Vilas | NR | Cause unknown | — |
| Lake Delton | Sauk | NR | Nutrients (phosphorus, nitrogen) | ✓ |
| Hallie Lake | Chippewa | NR | Turbidity | — |
| Pella Lake | Shawano | NR | Cause unknown | — |
| Lake Shangri-la | Kenosha | NR | Nutrients (phosphorus, nitrogen) | — |
| Voltz Lake | Kenosha | NR | Nutrients (phosphorus, nitrogen) | — |
| Ne Bay Lake | Vilas | NR | Cause unknown | — |
| Long Lake -Spread Eagle Chain | Florence | NR | Mercury | — |
| Clara Lake-Deep Hole | Lincoln | NR | Mercury | — |
| North Bay Lake | Vilas | NR | Cause unknown | — |
| Hodstradt Lake | Oneida | NR | Mercury | — |
| Swan Lake | Walworth | NR | Nutrients (phosphorus, nitrogen) | — |
| Swan Lake | Columbia | NR | Cause unknown | ✓ |
| High Falls Reservoir at | Marinette | NR | Mercury | — |
| Unnamed Rusk Co -Deep Hole Lake | Rusk | NR | Mercury | — |
| Seneca Lake | Vilas | NR | Nutrients (phosphorus, nitrogen) | — |
| Lake Thirty | Barron | NR | Nutrients (phosphorus, nitrogen) | — |
| Little Carr Lake | Oneida | NR | Mercury | — |
| Big Carr Lake | Oneida | NR | Mercury | — |
| Neshonoc Lake | La Crosse | NR | Mercury, Nutrients (phosphorus, nitrogen), Turbidity | — |
| Sheas Lake | Kewaunee | NR | Nutrients (phosphorus, nitrogen) | ✓ |
| Twin Falls Flowage Us Twin Falls Dam Lake | Florence | NR | Mercury | — |
| Madeline Lake | Oneida | NR | Mercury | — |
| Big Doctor Lake | Burnett | NR | Nutrients (phosphorus, nitrogen) | — |
| Catfish Lake | Vilas | NR | Cause unknown | — |
| Kettle Lake | Langlade | NR | Mercury | — |
| Hilbert Lake | Marinette | NR | Cause unknown | — |
| Morton Lake | Vilas | NR | Cause unknown | — |
| St. Louis River Outlet Upstream of John A. Blatnik Memorial Bridge Lake | Douglas | NR | Mercury, Metals (other than mercury), PCBs | — |
| Little Twin Lake | Green Lake | NR | Nutrients (phosphorus, nitrogen) | — |
| Prong Lake | Vilas | NR | Nutrients (phosphorus, nitrogen) | — |
| Smith Lake | Vilas | NR | Nutrients (phosphorus, nitrogen) | — |
| Range Line Lake | Vilas | NR | Cause unknown | — |
| Upper Clam Lake | Burnett | NR | Nutrients (phosphorus, nitrogen) | — |
| Pepin Lake | Pepin | NR | Nutrients (phosphorus, nitrogen) | — |
| Pokegama Lake | Barron | NR | Nutrients (phosphorus, nitrogen) | — |
| Hewitt Lake | Iron | NR | Mercury | — |
| Bittersweet Lake | Vilas | NR | Nutrients (phosphorus, nitrogen) | — |
| Carrol Lake | Oneida | NR | Nutrients (phosphorus, nitrogen) | — |
| Mcnutt Lake | Oneida | NR | Nutrients (phosphorus, nitrogen) | ✓ |
| Mead Lake Nb Test Site | Clark | NR | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Duluth Lake | Douglas | NR | Metals (other than mercury), Other cause, Toxic organics | — |
| South Harper Lake | Taylor | NR | Mercury | — |
| Blockhouse Lake | Price | NR | Nutrients (phosphorus, nitrogen) | — |
| Heidmann Lake | Kewaunee | NR | Nutrients (phosphorus, nitrogen) | ✓ |
| Little St Germain Lake-South Bay-Nr St Germain | Vilas | NR | Nutrients (phosphorus, nitrogen) | — |
| L St Germain Lake | Vilas | NR | Nutrients (phosphorus, nitrogen) | — |
| Lake Superior | Douglas | NR | Mercury, PFAS, PCBs | — |
| Park Lake | Columbia | NR | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Little Rice Lake | Forest | NR | Mercury | — |
| Calkins Lake | Chippewa | NR | Mercury | — |
| Little Yellow Lake | Burnett | NR | Nutrients (phosphorus, nitrogen) | — |
| Graber Pond | Dane | NR | Nutrients (phosphorus, nitrogen) | — |
| Lake of the Woods Barron Co. at | Barron | NR | Nutrients (phosphorus, nitrogen) | — |
| Trego Lake | Washburn | NR | Cause unknown | — |
| Tambling Lake | Vilas | NR | Cause unknown | — |
| Greater Bass Lake | Langlade | NR | Mercury | — |
| Lower Kelly Lake | Waukesha | NR | Nutrients (phosphorus, nitrogen) | — |
| Murdock Lake | Polk | NR | Nutrients (phosphorus, nitrogen) | — |
Frequently Asked Questions
How many lakes are impaired in Wisconsin?
473 of 1,353 graded Wisconsin lakes (35%) are listed as impaired in the most recent EPA ATTAINS reporting cycle. Of those, 424 are on the federal Clean Water Act §303(d) list and 61 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) (269 lakes); Mercury (129 lakes); Cause unknown (82 lakes); PCBs (15 lakes); Turbidity (13 lakes); Metals (other than mercury) (8 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.
More on impaired waters
Impaired Lakes Explained: What an EPA Listing Means
What it means when a lake is listed as impaired, why mercury is the most common reason, and why a listed lake can still be clear water with a good grade.
Mercury, PFAS, and the Fish You Shouldn't Eat
Why states issue fish-consumption advisories, which contaminants — mercury, PCBs, PFAS — drive them, and how to eat the fish you catch more safely.
Why Lakes Turn Green: Phosphorus and Nutrient Pollution
How phosphorus and nutrient runoff drive algae growth and turn lakes green, where the nutrients come from, and what it means for a lake's grade.
Lakes Making a Water-Quality Comeback
Which lakes are actually improving: multi-year EPA monitoring trends, the named recoveries still in progress, and what it takes to move a letter grade.
Data source
Impairment data from the EPA ATTAINS (Assessment and TMDL Tracking and Implementation System) public dataset. Assessment unit IDs are matched to LakeQuality lakes 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.