Impaired Lakes in Illinois
74 of 146 measured Illinois lakes (51%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 46 have an approved TMDL restoration plan.
Top Causes of Impairment in Illinois
Reading the Illinois impairment landscape
51% of Illinois's tracked lakes — 74 of 146 — 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 74 EPA-Listed Impaired Lakes in Illinois
| Lake | County | Causes | TMDL |
|---|---|---|---|
| Lake Opeka | Cook | Cause unknown | — |
| Lake Calumet | Cook | Mercury, Pesticides, PCBs | — |
| Powderhorn Lake | Cook | Mercury, Pesticides, PCBs | — |
| Catherine Lake | Lake | Mercury, Nutrients (phosphorus, nitrogen), PCBs | ✓ |
| Cedar Lake | Lake | Mercury, Pesticides | — |
| Deep Lake | Lake | Mercury, Pathogens (E. coli, fecal) | ✓ |
| Axehead Lake | Cook | Taste, color, odor | — |
| Boulder South Lake | Perry | Mercury | — |
| Shabbona Lake | DeKalb | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Channel Lake | Lake | Mercury, Nutrients (phosphorus, nitrogen), PCBs | ✓ |
| Zurich Lake | Lake | Mercury, Nutrients (phosphorus, nitrogen) | — |
| West Loon Lake | Lake | Mercury | — |
| Woods Creek Lake | McHenry | Nutrients (phosphorus, nitrogen), Pesticides, Turbidity | — |
| Kinkaid Lake | Jackson | Mercury | — |
| Tower Lake | Lake | Noxious aquatic plants, Nutrients (phosphorus, nitrogen), Pathogens (E. coli, fecal) +1 more | ✓ |
| East Loon Lake | Lake | Noxious aquatic plants, Nutrients (phosphorus, nitrogen) | — |
| Flatfoot Lake | Cook | Mercury | — |
| Tampier Lake | Cook | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Lake of Egypt | Williamson | Nutrients (phosphorus, nitrogen), Pesticides, PCBs | ✓ |
| Lily Lake | McHenry | Noxious aquatic plants, Nutrients (phosphorus, nitrogen) | — |
| Wesslyn Cut Lake | Perry | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Decatur Lake | Macon | Mercury, Metals (other than mercury), Nutrients (phosphorus, nitrogen) +2 more | ✓ |
| Olney East Fork Lake | Richland | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Vernor Lake | Richland | Algal growth, Mercury, Nutrients (phosphorus, nitrogen) | — |
| Fox Lake | Lake | Mercury, Nutrients (phosphorus, nitrogen), Pesticides +2 more | ✓ |
| Palmyra-Modesto Lake | Macoupin | Algal growth, Nutrients (phosphorus, nitrogen), Pesticides +3 more | ✓ |
| Greenfield Lake | Greene | Nutrients (phosphorus, nitrogen), Pesticides | — |
| Long Lake | Lake | Nutrients (phosphorus, nitrogen) | ✓ |
| Salem Lake | Marion | Mercury, Nutrients (phosphorus, nitrogen), Oxygen depletion (low DO) +2 more | ✓ |
| Vandalia Lake | Fayette | Mercury, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Bullfrog Lake | Cook | Algal growth, Noxious aquatic plants, Nutrients (phosphorus, nitrogen) +1 more | — |
| Holiday Shores Lake | Madison | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Dutchman Lake | Johnson | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Mermet Lake | Massac | Nutrients (phosphorus, nitrogen) | — |
| Skokie Lagoons Lake | Cook | Mercury, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Randolph Lake | Randolph | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Centralia Lake | Marion | Mercury, Nutrients (phosphorus, nitrogen), PCBs | ✓ |
| Sam Dale Lake | Wayne | Algal growth, Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Raccoon Lake | Marion | Mercury, Nutrients (phosphorus, nitrogen), Pesticides +1 more | ✓ |
| Carlyle Lake | Clinton | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Midlothian Lake | Cook | Mercury, Nutrients (phosphorus, nitrogen), Pesticides +1 more | — |
| Slm Side Channel Lake | St. Clair | Metals (other than mercury), Nutrients (phosphorus, nitrogen), Pesticides | — |
| Fairfield Lake | Wayne | Nutrients (phosphorus, nitrogen) | — |
| Glenn Shoals Lake | Montgomery | Algal growth, Mercury, Nutrients (phosphorus, nitrogen) +1 more | ✓ |
| Mattoon Lake | Cumberland | Algal growth, Mercury, Nutrients (phosphorus, nitrogen) +2 more | ✓ |
| Sara Lake | Effingham | Mercury, Metals (other than mercury), Nutrients (phosphorus, nitrogen) | ✓ |
| Otter Lake | Macoupin | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Lou Yaeger Lake | Montgomery | Mercury, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Grass Lake | Lake | Mercury, Nutrients (phosphorus, nitrogen), Pesticides +2 more | ✓ |
| Newton Lake | Jasper | Mercury, Nutrients (phosphorus, nitrogen) | ✓ |
| Nashville City Lake | Washington | Mercury, Nutrients (phosphorus, nitrogen), Pesticides | ✓ |
| Marie Lake | Lake | Mercury, Nutrients (phosphorus, nitrogen), PCBs | ✓ |
| Jacksonville Lake | Morgan | Mercury, Nutrients (phosphorus, nitrogen), Turbidity | — |
| Highland Silver Lake | Madison | Mercury, Nutrients (phosphorus, nitrogen), Pesticides | ✓ |
| Pistakee Lake | McHenry | Mercury, Nutrients (phosphorus, nitrogen), PCBs +1 more | ✓ |
| Canton Lake | Fulton | Mercury, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Kinmundy Old Lake | Marion | Cause unknown | ✓ |
| Nippersink Lake | Lake | Mercury, Nutrients (phosphorus, nitrogen), PCBs +1 more | ✓ |
| Kinmundy New Lake | Marion | Nutrients (phosphorus, nitrogen) | ✓ |
| Coulterville Lake | Randolph | Nutrients (phosphorus, nitrogen) | ✓ |
| Vermont City Lake | McDonough | Metals (other than mercury), Nutrients (phosphorus, nitrogen), Pesticides +1 more | ✓ |
| Mauvaise Terre Lake | Morgan | Mercury, Metals (other than mercury), Nutrients (phosphorus, nitrogen) +1 more | ✓ |
| Diamond Lake | Lake | Noxious aquatic plants, Nutrients (phosphorus, nitrogen) | ✓ |
| Valley Lake | Lake | Noxious aquatic plants, Nutrients (phosphorus, nitrogen), Turbidity | — |
| Louise Lake | Lake | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Slocum Lake | Lake | Noxious aquatic plants, Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Island Lake | McHenry | Nutrients (phosphorus, nitrogen), Turbidity | ✓ |
| Bull Frog Lake | Cook | Algal growth, Noxious aquatic plants, Nutrients (phosphorus, nitrogen) +1 more | — |
| Humboldt Park Lagoon Lake | Cook | Algal growth, Cause unknown, Mercury +2 more | — |
| Diversey Harbor Lake | Cook | Mercury, PCBs | ✓ |
| Loch Lomond Lake | Lake | Nutrients (phosphorus, nitrogen), Pathogens (E. coli, fecal), Turbidity | — |
| Hastings Lake | Lake | Nutrients (phosphorus, nitrogen), Pathogens (E. coli, fecal) | — |
| Petite Lake | Lake | Mercury, Nutrients (phosphorus, nitrogen), PCBs | ✓ |
| Bluff Lake | Lake | Mercury, Nutrients (phosphorus, nitrogen), PCBs | ✓ |
Frequently Asked Questions
How many lakes are impaired in Illinois?
74 of 146 measured Illinois lakes (51%) are listed as impaired in the most recent EPA ATTAINS reporting cycle. Of those, 69 are on the federal Clean Water Act §303(d) list and 46 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) (62 lakes); Mercury (46 lakes); Turbidity (27 lakes); Pesticides (17 lakes); PCBs (17 lakes); Noxious aquatic plants (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
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 favourable readings.
Why states issue fish-consumption advisories, which contaminants — mercury, PCBs, PFAS — drive them, and how to eat the fish you catch more safely.
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 readings.
Which lakes are actually improving: multi-year EPA monitoring trends, the named recoveries still in progress, and what it takes to move the readings.
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 Illinois's state water-quality agency.