Updated Aug 2026
Ohio Lake Water Quality
292 lakes across 81 counties, 43 with a recent water-quality reading.
Lake Map
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New water-quality readings for Ohio lakes as Ohio EPA publishes them. Unsubscribe anytime.
Where to stay near Ohio's cleanest lakes
Cabins, resorts, and vacation rentals around Marysville Upground Reservoir and the other cleanest Ohio lakes pinned on the map. Live availability and prices.
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Explore Ohio Lakes
Ohio reports, fishing & travel
Ohio's cleanest lakes, ranked on agency measurements
Species activity outlook by water temperature and season
Where to stay at Ohio's top lakes, each with its readings
Cleanest lakes within 50 miles of Columbus
Cleanest lakes within 50 miles of Cleveland
Reservoirs in Ohio
View all 6 reservoirs →6 of 292 Ohio lakes (2%) are man-made reservoirs in the USACE National Inventory of Dams. 6 carry a High or Significant hazard rating. The oldest matched dam dates to 1936.
EPA-Impaired Lakes in Ohio
View all 4 impaired lakes →4 of 292 Ohio lakes (1%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 2 have an approved Total Maximum Daily Load (TMDL) restoration plan.
Ohio Fishing & Recreation
Licenses, regulations, records, and where to fish across Ohio.
Counties
All 81 Ohio counties, ranked by average lake water quality. Compare them against every county nationwide in the county rankings, browse the full directory of lakes, or pick a different state.
Ohio Lake Water Quality Dataset (2026)
Every measured Ohio lake in one spreadsheet — water clarity, phosphorus, chlorophyll-a, trophic state, size, public access, and a link to each lake's page.
43 of the 292 Ohio lakes in this index carry a recent clarity, phosphorus or algae reading, spread over 81 counties. Those readings come from the Ohio Environmental Protection Agency, alongside federal programs and volunteer monitoring networks. The rest are listed for their size, depth and location, with no recent nutrient or algae sampling behind them. Most measured Ohio lakes are productive, often shallow, and frequently algal in late summer; each lake page shows its own phosphorus and chlorophyll-a readings.
Mosquito Creek Lake is the largest lake in this index at about 7,016 acres, one of 35 here that clear 500 acres. The rest run smaller, and small and shallow is where nutrient loading shows up first, because there is less water to dilute it and the bottom sediment stays within reach of the sun. A meaningful share of the state's measured lakes register as hypereutrophic: heavily nutrient-loaded, frequent blooms, low summer transparency. These are usually shallow, surrounded by row-crop agriculture, with little volume to buffer the inputs. The county with the lowest nutrient and algae readings on average is Union. The gap between counties is large enough that a single figure for Ohio lake water quality hides real local variation.
Lake Match
Which lake suits how you actually use one?
Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of lakes that fit, with the water quality behind each one.
Source: EPA National Aquatic Resource Surveys and the EPA Water Quality Portal.
More on lake water quality
A data snapshot of the lakes we track: the clearest and the greenest states, and where the water is improving.
How nutrient and algae readings are read against EPA ecoregion condition classes, what each class means in the water, and why a clean reading is not a clearance.
The clearest lakes in America, ranked by measured Secchi depth in feet from EPA monitoring data — and why the famously clear lakes are missing.