Updated Jul 2026
Ohio Lake Water Quality
Water quality grades for 17 monitored lakes across 13 counties.
Ohio has 17 graded lakes in our dataset, sampled across 13 counties, drawing on monitoring by the Ohio Environmental Protection Agency plus federal and volunteer measurements. A-grade lakes are scarce in Ohio: about 0% of the dataset. Most lakes here sit in C or D — productive, often shallow, frequently algal in late summer.
The state's lakes lean eutrophic: enough nutrient input to support an active algal community, with the trade-offs in clarity and dissolved oxygen that come with it. Lake ranks highest on average county grade (A). Ashland sits lowest. With only 13 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.
Grade Distribution
How Ohio’s 17 graded lakes break down from A (excellent) to F.
Top-Graded Ohio Lakes
The highest water-quality grades in Ohio — clarity, depth, and A-F grade at a glance.
Caesar Creek Lake
Warren County, Ohio
See grade for Caesar Creek Lake →Caesar Creek Lake
Warren County, Ohio
See grade for Caesar Creek Lake →Lake Vesuvius
Lawrence County, Ohio
See grade for Lake Vesuvius →Caesar Creek Lake
Warren County, Ohio
See grade for Caesar Creek Lake →Caesar Creek Lake
Warren County, Ohio
See grade for Caesar Creek Lake →Leesville Lake
Carroll County, Ohio
See grade for Leesville Lake →Sites Lake
Richland County, Ohio
See grade for Sites Lake →Tappan Lake
Harrison County, Ohio
See grade for Tappan Lake →Buck Creek Lake
Clark County, Ohio
See grade for Buck Creek Lake →Lake Map
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 10 reservoirs →10 of 17 Ohio lakes (59%) are man-made reservoirs in the USACE National Inventory of Dams. 10 carry a High or Significant hazard rating. The oldest matched dam dates to 1936.
EPA-Impaired Lakes in Ohio
View all 5 impaired lakes →5 of 17 Ohio lakes (29%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 4 have an approved Total Maximum Daily Load (TMDL) restoration plan.
Ohio Fishing & Recreation
Licenses, regulations, records, and where to fish across Ohio.
Counties
All 13 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.
Top 25 Cleanest Lakes
| Rank | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | Caesar Creek Lake | Warren | C | 3.8 ft |
| 2 | Caesar Creek Lake | Warren | C | 3.5 ft |
| 3 | Lake Vesuvius | Lawrence | C | 8.2 ft |
| 4 | Caesar Creek Lake | Warren | D | 3.2 ft |
| 5 | Caesar Creek Lake | Warren | D | 3 ft |
| 6 | Leesville Lake | Carroll | D | 5 ft |
| 7 | Sites Lake | Richland | D | 5.2 ft |
| 8 | Tappan Lake | Harrison | D | - |
| 9 | Buck Creek Lake | Clark | D | 2.5 ft |
| 10 | Buck Creek Lake | Clark | D | 2.3 ft |
| 11 | Buck Creek Lake | Clark | D | 2.1 ft |
| 12 | Buck Creek Lake | Clark | D | 2.5 ft |
| 13 | Charles Mill Reservoir | Ashland | F | 0.9 ft |
| 14 | Seneca Lake | Noble | F | 1.7 ft |
| 15 | Tappan Lake | Harrison | F | 1.8 ft |
| 16 | Clear Fork Reservoir | Morrow | F | 3.1 ft |
| 17 | Pleasant Hill Reservoir | Richland | F | 3 ft |
25 Lakes Needing Attention
| Rank | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | Pleasant Hill Reservoir | Richland | F | 3 ft |
| 2 | Clear Fork Reservoir | Morrow | F | 3.1 ft |
| 3 | Tappan Lake | Harrison | F | 1.8 ft |
| 4 | Seneca Lake | Noble | F | 1.7 ft |
| 5 | Charles Mill Reservoir | Ashland | F | 0.9 ft |
| 6 | Buck Creek Lake | Clark | D | 2.5 ft |
| 7 | Buck Creek Lake | Clark | D | 2.1 ft |
| 8 | Buck Creek Lake | Clark | D | 2.3 ft |
| 9 | Buck Creek Lake | Clark | D | 2.5 ft |
| 10 | Tappan Lake | Harrison | D | - |
| 11 | Sites Lake | Richland | D | 5.2 ft |
| 12 | Leesville Lake | Carroll | D | 5 ft |
| 13 | Caesar Creek Lake | Warren | D | 3 ft |
| 14 | Caesar Creek Lake | Warren | D | 3.2 ft |
| 15 | Lake Vesuvius | Lawrence | C | 8.2 ft |
| 16 | Caesar Creek Lake | Warren | C | 3.5 ft |
| 17 | Caesar Creek Lake | Warren | C | 3.8 ft |
Where to stay near Ohio
Top-rated places to stay near Ohio
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Source: EPA National Aquatic Resource Surveys, 2026.