Impaired Lakes in Illinois
112 of 144 graded Illinois lakes (78%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 52 have an approved TMDL restoration plan.
Top Causes of Impairment in Illinois
Reading the Illinois impairment landscape
78% of Illinois's tracked lakes — 112 of 144 — appear on the EPA Clean Water Act §303(d) impaired-waters list. At that share, impairment is the default state rather than an exception: the majority of lakes are flagged for at least one pollutant exceeding water-quality standards. Trip-planning for clean water in Illinois typically requires checking impairment status as a first filter, not as an edge case.
The leading impairment category in Illinois 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 Illinois submission to the EPA Assessment, Total Maximum Daily Load Tracking and Implementation System (ATTAINS) dataset.
All 112 EPA-Listed Impaired Lakes in Illinois
| Lake | County | Grade | Causes | TMDL |
|---|---|---|---|---|
| Diversey Harbor Lake | Cook | A | Mercury, PCBs | ✓ |
| Loch Lomond Lake | Lake | A | Nutrients (phosphorus, nitrogen), Pathogens (E. coli, fecal), Turbidity | — |
| Axehead Lake | Cook | A | Taste, color, odor | — |
| Powderhorn Lake | Cook | A | Mercury, Pesticides, PCBs | — |
| Silver Lake | McHenry | B | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Silver Lake | McHenry | B | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Timber Lake | Lake | B | Noxious aquatic plants, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Boulder South Lake | Perry | B | Mercury | — |
| Round Lake | Lake | B | Nutrients (phosphorus, nitrogen) | — |
| Kinkaid Lake | Jackson | B | Mercury | — |
| Lake Calumet | Cook | B | Mercury, Pesticides, PCBs | — |
| Flatfoot Lake | Cook | B | Mercury | — |
| Opeka Lake | Cook | B | Cause unknown | — |
| Glendale Lake | Pope | B | Turbidity | — |
| Grays Lake | Lake | B | Noxious aquatic plants, Nutrients (phosphorus, nitrogen) | — |
| Calumet Lake | Cook | B | Mercury, Pesticides, PCBs | — |
| Lily Lake | McHenry | B | Noxious aquatic plants, Nutrients (phosphorus, nitrogen) | — |
| Catherine Lake | Lake | B | Mercury, Nutrients (phosphorus, nitrogen), PCBs | ✓ |
| George Lake | Rock Island | C | Mercury, Nutrients (phosphorus, nitrogen), Turbidity | — |
| Shabbona Lake | DeKalb | C | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Channel Lake | Lake | C | Mercury, Nutrients (phosphorus, nitrogen), PCBs | ✓ |
| Palmyra-Modesto Lake | Macoupin | C | Algal growth, Nutrients (phosphorus, nitrogen), Pesticides +3 more | ✓ |
| Lake of Egypt | Williamson | C | Nutrients (phosphorus, nitrogen), Pesticides, PCBs | ✓ |
| Turtlehead Lake | Cook | C | Cause unknown, Mercury | — |
| Olney East Fork Lake | Richland | C | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Woods Creek Lake | McHenry | C | Nutrients (phosphorus, nitrogen), Pesticides, Turbidity | — |
| Lake Opeka | Cook | D | Cause unknown | — |
| Flatfoot Lake | Cook | D | Mercury | — |
| Maple Lake | Cook | D | Algal growth, Noxious aquatic plants, Nutrients (phosphorus, nitrogen) +1 more | — |
| Busse Lake Main Pool | Cook | D | Mercury, Nutrients (phosphorus, nitrogen), Pathogens (E. coli, fecal) +2 more | — |
| Pogie Lake | Cook | D | Mercury, Nutrients (phosphorus, nitrogen), Pesticides +1 more | — |
| Columbia Basin Lake | Cook | D | Nutrients (phosphorus, nitrogen) | — |
| Jackson Park Inner Harbor Lake | Cook | D | Mercury, PCBs | — |
| Turtlehead Lake | Cook | D | Cause unknown, Mercury | — |
| Jackson Park West Lagoon Lake | Cook | D | Nutrients (phosphorus, nitrogen) | — |
| Jackson Park Outer Harbor Lake | Cook | D | Mercury, PCBs | — |
| South Pond | Cook | D | Algal growth, Nutrients (phosphorus, nitrogen), Turbidity | — |
| Jackson Park East Lagoon Lake | Cook | D | Nutrients (phosphorus, nitrogen) | — |
| Long Lake | Lake | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Arrowhead Lake | Cook | D | Cause unknown, Mercury | — |
| Bullfrog Lake | Cook | D | Algal growth, Noxious aquatic plants, Nutrients (phosphorus, nitrogen) +1 more | — |
| Hastings Lake | Lake | D | Nutrients (phosphorus, nitrogen), Pathogens (E. coli, fecal) | — |
| Dutchman Lake | Johnson | D | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Randolph Lake | Randolph | D | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Wayne City Lake | Wayne | D | Cause unknown, Nutrients (phosphorus, nitrogen) | ✓ |
| Tampier Lake | Cook | D | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Midlothian Lake | Cook | D | Mercury, Nutrients (phosphorus, nitrogen), Pesticides +1 more | — |
| Sparta Northwest Lake | Randolph | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Sara Lake | Effingham | D | Mercury, Metals (other than mercury), Nutrients (phosphorus, nitrogen) | ✓ |
| Otter Lake | Macoupin | D | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Grass Lake | Lake | D | Mercury, Nutrients (phosphorus, nitrogen), Pesticides +2 more | ✓ |
| Jacksonville Lake | Morgan | D | Mercury, Nutrients (phosphorus, nitrogen), Turbidity | — |
| Long Lake | Lake | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Fox Lake | Lake | D | Mercury, Nutrients (phosphorus, nitrogen), Pesticides +2 more | ✓ |
| Petite Lake | Lake | D | Mercury, Nutrients (phosphorus, nitrogen), PCBs | ✓ |
| Canton Lake | Fulton | D | Mercury, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Nippersink Lake | Lake | D | Mercury, Nutrients (phosphorus, nitrogen), PCBs +1 more | ✓ |
| Kinmundy New Lake | Marion | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Charleston Side Channel Lake | Coles | D | Nutrients (phosphorus, nitrogen) | ✓ |
| Loveless Lake | Macoupin | D | Nutrients (phosphorus, nitrogen), Pesticides | — |
| Greenfield Lake | Greene | D | Nutrients (phosphorus, nitrogen), Pesticides | — |
| Forbes Lake | Marion | D | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Mermet Lake | Massac | D | Nutrients (phosphorus, nitrogen) | — |
| Centralia Lake | Marion | D | Mercury, Nutrients (phosphorus, nitrogen), PCBs | ✓ |
| Wesslyn Cut Lake | Perry | D | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Newton Lake | Jasper | D | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Marie Lake | Lake | D | Mercury, Nutrients (phosphorus, nitrogen), PCBs | ✓ |
| Monee Lake | Will | D | Mercury, Nutrients (phosphorus, nitrogen), Pesticides | — |
| Vernor Lake | Richland | D | Algal growth, Mercury, Nutrients (phosphorus, nitrogen) | — |
| Pistakee Lake | McHenry | D | Mercury, Nutrients (phosphorus, nitrogen), PCBs +1 more | ✓ |
| Bluff Lake | Lake | D | Mercury, Nutrients (phosphorus, nitrogen), PCBs | ✓ |
| Bull Frog Lake | Cook | F | Algal growth, Noxious aquatic plants, Nutrients (phosphorus, nitrogen) +1 more | — |
| Sauk Lake | Cook | F | Algal growth, Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) +3 more | ✓ |
| North Pond | Cook | F | Algal growth, Nutrients (phosphorus, nitrogen), Turbidity | — |
| Washington Park Lagoon Lake | Cook | F | Algal growth, Nutrients (phosphorus, nitrogen), Turbidity | — |
| Sherman Park Lagoon Lake | Cook | F | Cause unknown, Mercury | — |
| Tampier Lake | Cook | F | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Humboldt Park Lagoon Lake | Cook | F | Algal growth, Cause unknown, Mercury +2 more | — |
| Big Marsh Park Ne Lake | Cook | F | Mercury, Pesticides, PCBs | — |
| Garfield Park Lagoon Lake | Cook | F | Cause unknown, Turbidity | — |
| Douglass Park Lagoon Lake | Cook | F | Cause unknown, Turbidity | — |
| Mckinley Park Lagoon Lake | Cook | F | Mercury, PCBs | — |
| Columbus Park Lagoon Lake | Cook | F | Cause unknown | — |
| Marquette Park Lagoon Lake | Cook | F | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Burnham Prairie Marsh West Lake | Cook | F | Mercury, Pesticides, PCBs | — |
| Big Marsh Lake | Cook | F | Mercury, Pesticides, PCBs | — |
| Lake Calumet | Cook | F | Mercury, Pesticides, PCBs | — |
| Salem Lake | Marion | F | Mercury, Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) +2 more | ✓ |
| Saganashkee Slough Lake | Cook | F | Algal growth, Metals (other than mercury), Nutrients (phosphorus, nitrogen) +3 more | ✓ |
| Vandalia Lake | Fayette | F | Mercury, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Holiday Shores Lake | Madison | F | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Skokie Lagoons Lake | Cook | F | Mercury, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Sam Dale Lake | Wayne | F | Algal growth, Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Raccoon Lake | Marion | F | Mercury, Nutrients (phosphorus, nitrogen), Pesticides +1 more | ✓ |
| Carlyle Lake | Clinton | F | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Slm Side Channel Lake | St. Clair | F | Metals (other than mercury), Nutrients (phosphorus, nitrogen), Pesticides | — |
| Fairfield Lake | Wayne | F | Nutrients (phosphorus, nitrogen) | — |
| Glenn Shoals Lake | Montgomery | F | Algal growth, Mercury, Nutrients (phosphorus, nitrogen) +1 more | ✓ |
| Mattoon Lake | Cumberland | F | Algal growth, Mercury, Nutrients (phosphorus, nitrogen) +2 more | ✓ |
| Lou Yaeger Lake | Montgomery | F | Mercury, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Decatur Lake | Macon | F | Mercury, Metals (other than mercury), Nutrients (phosphorus, nitrogen) +2 more | ✓ |
| Governor Bond Lake | Bond | F | Mercury, Nutrients (phosphorus, nitrogen), Pesticides | ✓ |
| Nashville City Lake | Washington | F | Mercury, Nutrients (phosphorus, nitrogen), Pesticides | ✓ |
| Highland Silver Lake | Madison | F | Mercury, Nutrients (phosphorus, nitrogen), Pesticides | ✓ |
| Borah Lake | Richland | F | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Kinmundy Old Lake | Marion | F | Cause unknown | ✓ |
| Coulterville Lake | Randolph | F | Nutrients (phosphorus, nitrogen) | ✓ |
| Paradise Lake | Pike | F | Algal growth, Mercury, Nutrients (phosphorus, nitrogen) +1 more | — |
| Paradise Lake | Coles | F | Algal growth, Mercury, Metals (other than mercury) +4 more | ✓ |
| Vermont City Lake | McDonough | F | Metals (other than mercury), Nutrients (phosphorus, nitrogen), Pesticides +1 more | ✓ |
| Mauvaise Terre Lake | Morgan | F | Mercury, Metals (other than mercury), Nutrients (phosphorus, nitrogen) +1 more | ✓ |
| Quiver Lake | Mason | F | Mercury, Pesticides | — |
Frequently Asked Questions
How many lakes are impaired in Illinois?
112 of 144 graded Illinois lakes (78%) are listed as impaired in the most recent EPA ATTAINS reporting cycle. Of those, 105 are on the federal Clean Water Act §303(d) list and 52 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 Illinois?
The most common causes flagged across Illinois's impaired lakes are: Nutrients (phosphorus, nitrogen) (84 lakes); Mercury (68 lakes); Turbidity (37 lakes); PCBs (29 lakes); Pesticides (26 lakes); Algal growth (16 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 Illinois's state water-quality agency.