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LakeQuality

Data Report · Updated July 2026

The State of Ohio’s Lakes 2026

Of 17 monitored lakes in Ohio, 0% earn a water-quality grade of A or B and 82.4% score D or F (average grade D). Caesar Creek Lake is the cleanest; 5 lakes (29.4%) are on an official impaired-waters list.

17
Monitored lakes graded
D
Average grade
0%
Grade A or B
29.4%
On impaired list

Ohio grade distribution

C
D
F
A: 0 (0.0%)B: 0 (0.0%)C: 3 (17.6%)D: 9 (52.9%)F: 5 (29.4%)

Cleanest lakes in Ohio

Highest combined water-quality score, 2026.

  1. 1.CCaesar Creek Lake — Warren County3.8 ft clarity · 18 µg/L P · 24 µg/L chl-a
  2. 2.CCaesar Creek Lake — Warren County3.5 ft clarity · 25 µg/L P · 19 µg/L chl-a
  3. 3.DCaesar Creek Lake — Warren County3.2 ft clarity · 26 µg/L P · 20 µg/L chl-a
  4. 4.DCaesar Creek Lake — Warren County3.0 ft clarity · 27 µg/L P · 23 µg/L chl-a
  5. 5.DBuck Creek Lake — Clark County2.5 ft clarity · 42 µg/L P · 37 µg/L chl-a
  6. 6.DBuck Creek Lake — Clark County2.3 ft clarity · 44 µg/L P · 40 µg/L chl-a
  7. 7.DBuck Creek Lake — Clark County2.1 ft clarity · 45 µg/L P · 36 µg/L chl-a
  8. 8.DBuck Creek Lake — Clark County2.5 ft clarity · 41 µg/L P · 40 µg/L chl-a

Most-polluted lakes

Lowest combined water-quality score among monitored lakes.

  1. 1.DBuck Creek Lake — Clark County2.5 ft clarity · 42 µg/L P · 37 µg/L chl-a
  2. 2.DBuck Creek Lake — Clark County2.3 ft clarity · 44 µg/L P · 40 µg/L chl-a
  3. 3.DBuck Creek Lake — Clark County2.1 ft clarity · 45 µg/L P · 36 µg/L chl-a
  4. 4.DBuck Creek Lake — Clark County2.5 ft clarity · 41 µg/L P · 40 µg/L chl-a
  5. 5.DCaesar Creek Lake — Warren County3.2 ft clarity · 26 µg/L P · 20 µg/L chl-a
  6. 6.DCaesar Creek Lake — Warren County3.0 ft clarity · 27 µg/L P · 23 µg/L chl-a
  7. 7.CCaesar Creek Lake — Warren County3.8 ft clarity · 18 µg/L P · 24 µg/L chl-a
  8. 8.CCaesar Creek Lake — Warren County3.5 ft clarity · 25 µg/L P · 19 µg/L chl-a

Worst algae hotspots

Highest measured chlorophyll-a (algae) concentration.

  1. 1.DBuck Creek Lake — Clark County40 µg/L chlorophyll-a
  2. 2.DBuck Creek Lake — Clark County40 µg/L chlorophyll-a
  3. 3.DBuck Creek Lake — Clark County37 µg/L chlorophyll-a
  4. 4.DBuck Creek Lake — Clark County36 µg/L chlorophyll-a
  5. 5.CCaesar Creek Lake — Warren County24 µg/L chlorophyll-a
  6. 6.DCaesar Creek Lake — Warren County23 µg/L chlorophyll-a
  7. 7.DCaesar Creek Lake — Warren County20 µg/L chlorophyll-a

Trending lakes

Improving

  1. 1.DSites Lake — Richland County
  2. 2.FCharles Mill Reservoir — Ashland County

Declining

  1. 1.DTappan Lake — Harrison County
  2. 2.DCaesar Creek Lake — Warren County
  3. 3.DCaesar Creek Lake — Warren County
  4. 4.CCaesar Creek Lake — Warren County
  5. 5.CCaesar Creek Lake — Warren County

Impaired waters in Ohio

5 lakes appear on the EPA/state 303(d) impaired-waters list (4 formally listed, 4 with a cleanup plan/TMDL).

Algal growth · 3Other cause · 1Habitat alterations · 1Hydrologic alteration · 1Metals (other than mercury) · 1pH / acidity · 1Sediment / turbidity · 1

Grades combine Secchi clarity, total phosphorus, and chlorophyll-a from the EPA Water Quality Portal and state agencies. See the full methodology, the national State of America’s Lakes report, or all Ohio lakes.

Cite this report: LakeQuality, “The State of Ohio’s Lakes 2026,” lakequality.org/report/oh.