Impaired Lakes in Ohio
14 of 44 graded Ohio lakes (32%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 11 have an approved TMDL restoration plan.
Top Causes of Impairment in Ohio
Reading the Ohio impairment landscape
Ohio reports 14 impaired lakes — 32% of the state's 44 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.
Pathogen impairment (Pathogens (E. coli, fecal)) leads the Ohio list — typically from agricultural runoff, failing septic systems, urban stormwater, or wildlife sources. Pathogen-impaired waters are the highest-risk category for body-contact recreation: bacterial counts can spike during and after rain events, exceeding swimming standards. Check the state's beach-water advisories for posted closures, particularly within 48 hours of significant rainfall.
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 Ohio submission to the EPA Assessment, Total Maximum Daily Load Tracking and Implementation System (ATTAINS) dataset.
All 14 EPA-Listed Impaired Lakes in Ohio
| Lake | County | Grade | Causes | TMDL |
|---|---|---|---|---|
| Powers Reservoir | Crawford | B | Habitat alterations, Hydrologic alteration, Nutrients (phosphorus, nitrogen) +2 more | ✓ |
| Lost Creek Reservoir | Allen | B | Algal growth, Fish kills (cause unknown), Nutrients (phosphorus, nitrogen) +1 more | ✓ |
| New Lexington Reservoir | Perry | C | Habitat alterations, Metals (other than mercury), Nutrients (phosphorus, nitrogen) +5 more | ✓ |
| Ottawa R Lake | Allen | C | Cause unknown, Habitat alterations, Nutrients (phosphorus, nitrogen) +2 more | ✓ |
| Ferguson Reservoir | Allen | C | Algal growth, Ammonia, Cause unknown +7 more | ✓ |
| Caesar Creek Lake | Warren | D | Algal growth, Other cause | ✓ |
| Salem Reservoir | Columbiana | D | Pathogens (E. coli, fecal) | — |
| Metzger Reservoir | Allen | D | Algal growth, Ammonia, Cause unknown +7 more | ✓ |
| Amann Reservoir | Morrow | D | Habitat alterations, Hydrologic alteration, Nutrients (phosphorus, nitrogen) +2 more | ✓ |
| Auglaize R Lake | Paulding | F | Hydrologic alteration, Pathogens (E. coli, fecal), Sediment / turbidity | — |
| Somerset Reservoir | Perry | F | Habitat alterations, Metals (other than mercury), Nutrients (phosphorus, nitrogen) +5 more | ✓ |
| St Joseph Lake | Perry | F | Habitat alterations, Metals (other than mercury), Nutrients (phosphorus, nitrogen) +5 more | ✓ |
| Lake Vesuvius | Lawrence | NR | Metals (other than mercury), pH / acidity, Sediment / turbidity | — |
| Tappan Lake @ Cadiz Public Water Supply Intake | Harrison | NR | Algal growth | ✓ |
Frequently Asked Questions
How many lakes are impaired in Ohio?
14 of 44 graded Ohio lakes (32%) are listed as impaired in the most recent EPA ATTAINS reporting cycle. Of those, 12 are on the federal Clean Water Act §303(d) list and 11 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 Ohio?
The most common causes flagged across Ohio's impaired lakes are: Pathogens (E. coli, fecal) (10 lakes); Sediment / turbidity (9 lakes); Nutrients (phosphorus, nitrogen) (9 lakes); Habitat alterations (8 lakes); Oxygen depletion (low DO) (7 lakes); Algal growth (5 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 a good grade.
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 grade.
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 Ohio's state water-quality agency.