Updated Aug 2026
Ohio Lake Water Quality
Water quality grades for 31 of the 292 lakes we list here, across 81 counties.
Grade Distribution
All 292 Ohio lakes in the index: 31 (10.6%) carry an A–F grade and 261 (89.4%) are not rated, because they lack enough recent nutrient or algae sampling to support a letter.
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Where to stay near Ohio's top-graded lakes
Cabins, resorts, and vacation rentals around Marysville Upground Reservoir and the other top-graded Ohio lakes pinned on the map. Live availability and prices.
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Explore Ohio Lakes
Ohio reports, fishing & travel
Ohio's cleanest and most-polluted lakes, ranked A–F
Species activity outlook by water temperature and season
Where to stay at Ohio's top lakes, each with its grade
Best-graded lakes within 50 miles of Columbus
Best-graded 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 14 impaired lakes →14 of 292 Ohio lakes (5%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 11 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 graded lakes, or pick a different state.
Ohio Lake Water Quality Dataset (2026)
Every graded Ohio lake in one spreadsheet — A–F grade, water clarity, phosphorus, chlorophyll-a, trophic state, size, public access, and a link to each lake's report card.
25 Lakes Needing Attention
25 lakes25 graded lakes
| # | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | FHoover Reservoir | Delaware | F | No recent samples |
| 2 | FBresler Reservoir | Allen | F | No recent samples |
| 3 | FO'Shaughnessy Reservoir Lake | Delaware | F | No recent samples |
| 4 | FAmicks Reservoir | Morrow | F | No recent samples |
| 5 | FAlum Creek Lake | Delaware | F | No recent samples |
| 6 | FSt Joseph Lake | Perry | F | No recent samples |
| 7 | FGrand Lake St Marys @ Intake | Mercer | F | No recent samples |
| 8 | FSomerset Reservoir | Perry | F | No recent samples |
| 9 | FSpring Valley Lake Lake | Columbiana | F | No recent samples |
| 10 | FAuglaize R Lake | Paulding | F | No recent samples |
| 11 | FBuck Creek Lake | Clark | F | 2.5 ft |
| 12 | DAmann Reservoir | Morrow | D | No recent samples |
| 13 | DOttawa Reservoir | Putnam | D | No recent samples |
| 14 | DTwin Lakes Reservoir | Allen | D | No recent samples |
| 15 | DMetzger Reservoir | Allen | D | No recent samples |
| 16 | DSalem Reservoir | Columbiana | D | No recent samples |
| 17 | DLake Logan | Hocking | D | No recent samples |
| 18 | DBurr Oak Reservoir | Morgan | D | No recent samples |
| 19 | DUpper Sandusky Reservoir | Wyandot | D | No recent samples |
| 20 | DMaumee R Upst Independence Dam Lake | Defiance | D | No recent samples |
| 21 | DCaesar Creek Lake | Warren | D | 3.2 ft |
| 22 | CWilliams Reservoir | Allen | C | No recent samples |
| 23 | CFerguson Reservoir | Allen | C | No recent samples |
| 24 | COttawa R Lake | Allen | C | No recent samples |
| 25 | CFindlay Reservoir | Hancock | C | No recent samples |
31 of the 292 Ohio lakes in this index carry an A–F water-quality grade, spread over 81 counties. Those grades rest on measurements from the Ohio Environmental Protection Agency, alongside federal programs and volunteer monitoring networks. The rest are listed for their size, depth and location, without enough recent nutrient or algae sampling behind them to support a letter. A-grade lakes are scarce among the Ohio lakes that carry a letter: about 3% of them. Most sit in C or D, productive, often shallow, frequently algal in late summer.
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 graded 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 cleanest county on average is Union (grade A); the most-stressed is Delaware. The gap between the top and bottom 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 graded 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 grade: how the A–F distribution breaks down, the clearest and the greenest states, and where the water is improving.
How lakes are graded A–F on nutrients and algae using EPA ecoregion condition classes, what each letter means in the water, and why an A is not a clearance.
The cleanest and dirtiest U.S. lakes in the monitoring record, ranked on EPA nutrient and algae condition classes across thousands of graded lakes.
The clearest lakes in America, ranked by measured Secchi depth in feet from EPA monitoring data — and why the famously clear lakes are missing.