Impaired Lakes in Iowa
66 of 189 measured Iowa lakes (35%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 41 have an approved TMDL restoration plan.
Top Causes of Impairment in Iowa
Reading the Iowa impairment landscape
Iowa reports 66 impaired lakes — 35% of the state's 189 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 cause in Iowa is Turbidity. Each impairment category carries its own use-restriction implications — some affect fish consumption, some affect swimming, some affect aquatic-life habitat. Click through to the specific lake records below for the pollutant list and the TMDL (Total Maximum Daily Load) status, which determines whether a cleanup plan is in place.
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 Iowa submission to the EPA Assessment, Total Maximum Daily Load Tracking and Implementation System (ATTAINS) dataset.
All 66 EPA-Listed Impaired Lakes in Iowa
| Lake | County | Causes | TMDL |
|---|---|---|---|
| Mariposa Lake | Jasper | Algal growth, Turbidity | ✓ |
| Mormon Trail Lake | Adair | Mercury | — |
| Bob White Lake | Wayne | Turbidity | ✓ |
| Poll Miller Park Lake | Lee | Mercury | — |
| Lake of the Hills | Scott | Algal growth | ✓ |
| Nodaway Lake | Adair | Turbidity | — |
| Loch Ayr Lake | Ringgold | Turbidity | — |
| Clear Lake | Cerro Gordo | Pathogens (E. coli, fecal), Turbidity | ✓ |
| Lake Cornelia | Wright | Turbidity | ✓ |
| Hawthorn Lake | Mahaska | Algal growth | ✓ |
| Otter Creek Lake | Tama | Algal growth, Turbidity | ✓ |
| East Okoboji Lake | Dickinson | Mercury | — |
| West Lake Osceola | Clarke | Oxygen depletion (low DO) | — |
| Spring Lake | Cherokee | Turbidity | — |
| Gustafson Lake | Buena Vista | Pathogens (E. coli, fecal), Turbidity | — |
| Hickory Grove Lake | Story | Pathogens (E. coli, fecal), Turbidity | ✓ |
| Snyder Bend Lake | Woodbury | Algal growth, Turbidity | — |
| Big Creek Lake | Polk | Algal growth, Pathogens (E. coli, fecal) | ✓ |
| Arrowhead Lake | Pottawattamie | Algal growth, Turbidity | ✓ |
| Hannen Lake | Benton | Algal growth | ✓ |
| Briggs Woods Lake | Hamilton | Algal growth, pH / acidity, Turbidity | ✓ |
| Grays Lake | Polk | Algal growth, Turbidity | — |
| Union Grove Lake | Tama | Algal growth, Pathogens (E. coli, fecal), pH / acidity +1 more | ✓ |
| Littlefield Lake | Audubon | Algal growth, Turbidity | ✓ |
| Meyers Lake | Black Hawk | Algal growth | — |
| Diamond Lake | Poweshiek | Algal growth | — |
| Badger Lake | Webster | Turbidity | — |
| Blue Heron Lake | Polk | Turbidity | — |
| Upper Pine Lake | Hardin | Algal growth | ✓ |
| Crawford Creek Lake | Ida | pH / acidity | — |
| Green Valley Lake | Union | Algal growth, Oxygen depletion (low DO), pH / acidity +1 more | ✓ |
| Meadow Lake | Adair | Algal growth, Turbidity | ✓ |
| East Lake Osceola | Clarke | Oxygen depletion (low DO), Turbidity | ✓ |
| Lake Iowa | Iowa | Algal growth, Mercury, Pathogens (E. coli, fecal) | ✓ |
| Don Williams Lake | Boone | Algal growth, Sediment / turbidity, Turbidity | ✓ |
| Silver Lake | Palo Alto | Algal growth, Turbidity | ✓ |
| Little Wall Lake | Hamilton | Algal growth, Turbidity | ✓ |
| Morris Lake | Lucas | Oxygen depletion (low DO) | — |
| Lake Orient | Adair | Algal growth, pH / acidity, Turbidity | ✓ |
| Lake Anita | Cass | Turbidity | ✓ |
| Roberts Creek Lake | Marion | Turbidity | — |
| Prairie Rose Lake | Shelby | Algal growth, Pathogens (E. coli, fecal), Turbidity | ✓ |
| Center Lake | Dickinson | Turbidity | — |
| Lower Pine Lake | Hardin | Algal growth, Pathogens (E. coli, fecal) | ✓ |
| Mckinley Lake | Union | Algal growth, PCBs, Turbidity | — |
| Brushy Creek Lake | Webster | Pathogens (E. coli, fecal) | ✓ |
| Lake Icaria | Adams | Turbidity | ✓ |
| Red Haw Lake | Lucas | Mercury | — |
| Beaver Lake | Dallas | Algal growth, pH / acidity | ✓ |
| Fin And Feather Lake | Cerro Gordo | pH / acidity | — |
| Five Island Lake | Palo Alto | Algal growth, Turbidity | ✓ |
| Avenue of the Saints Lake | Bremer | Algal growth, pH / acidity, Turbidity | ✓ |
| Desoto Bend Lake | Harrison | Algal growth, Turbidity | — |
| Eldred Sherwood Lake | Hancock | Pathogens (E. coli, fecal) | ✓ |
| Lake Manawa | Pottawattamie | Pathogens (E. coli, fecal), Turbidity | — |
| Big Hollow Lake | Des Moines | Algal growth, pH / acidity, Turbidity | ✓ |
| Lake Geode | Des Moines | Mercury, Pathogens (E. coli, fecal), pH / acidity | ✓ |
| Browns Lake | Woodbury | Turbidity | — |
| Indian Lake | Van Buren | Turbidity | ✓ |
| Ingham Lake | Emmet | Algal growth, Turbidity | ✓ |
| Smith Lake | Kossuth | Algal growth | ✓ |
| Lake Hendricks | Howard | Algal growth | — |
| Windmill Lake | Taylor | Turbidity | ✓ |
| Pierce Creek Lake | Page | Algal growth, Turbidity | ✓ |
| Lake Pahoja | Lyon | Pathogens (E. coli, fecal) | ✓ |
| Corydon Reservoir | Wayne | Pesticides | ✓ |
Frequently Asked Questions
How many lakes are impaired in Iowa?
66 of 189 measured Iowa lakes (35%) are listed as impaired in the most recent EPA ATTAINS reporting cycle. Of those, 40 are on the federal Clean Water Act §303(d) list and 41 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 Iowa?
The most common causes flagged across Iowa's impaired lakes are: Turbidity (41 lakes); Algal growth (34 lakes); Pathogens (E. coli, fecal) (13 lakes); pH / acidity (10 lakes); Mercury (6 lakes); Oxygen depletion (low DO) (4 lakes). Mercury is widespread in fish tissue across the upper Midwest from atmospheric deposition. Nutrient impairment (phosphorus, nitrogen) typically reflects agricultural runoff and urban stormwater.
Can I swim in an impaired lake?
It depends on the cause of impairment. A lake impaired for "mercury in fish tissue" is generally safe to swim in — the warning is about long-term consumption of fish. A lake impaired for "pathogens" (E. coli) or "algal growth" may pose a swimming risk and often has a separate beach advisory. Check the cause categories listed for each lake below, and consult your state health department's beach monitoring program for current advisories.
Where does this impairment data come from?
Every impairment record on this page comes from the EPA's ATTAINS (Assessment and TMDL Tracking and Implementation System) public dataset, the federal repository of state-reported water quality assessments. EPA ATTAINS is published as GeoParquet files on the EPA Office of Water S3 bucket and refreshed several times per year. Causes and use-support codes follow EPA's standard taxonomy.
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 Iowa's state water-quality agency.