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LakeQuality
Pink and orange afterglow over the treeline on Slim Lake after sunset

Updated August 2026

The State of Ohio's Lakes 2026

Of 44 lakes in Ohio, 9.7% sit in EPA's favourable condition classes for nutrients and algae and 67.7% in its poorer ones. Caesar Creek Lake is the cleanest; 14 lakes (31.8%) are on an official impaired-waters list.

Data Report

44
Monitored lakes sampled
D
Average readings
9.7%
low nutrient and algae readings
31.8%
On impaired list

Ohio nutrient and algae readings

Cleanest lakes in Ohio

Cleanest combined nutrient and algae readings, 2026.

  1. 1.Caesar Creek Lake — Warren County3.2 ft clarity · 25 µg/L P · 20 µg/L chl-a

Highest measured algae

Highest measured chlorophyll-a (algae) concentration.

  1. 1.Grand Lake St Marys @ Intake — Mercer County117 µg/L chlorophyll-a
  2. 2.Spring Valley Lake Lake — Columbiana County84 µg/L chlorophyll-a
  3. 3.Auglaize R Lake — Paulding County73 µg/L chlorophyll-a
  4. 4.Tappan Lake @ Cadiz Public Water Supply Intake — Harrison County72 µg/L chlorophyll-a
  5. 5.Hoover Reservoir — Delaware County70 µg/L chlorophyll-a
  6. 6.Tapan Lake Adj To Marina — Harrison County65 µg/L chlorophyll-a
  7. 7.Somerset Reservoir — Perry County64 µg/L chlorophyll-a
  8. 8.St Joseph Lake — Perry County59 µg/L chlorophyll-a
  9. 9.Alum Creek Lake — Delaware County54 µg/L chlorophyll-a
  10. 10.Maumee R Upst Independence Dam Lake — Defiance County51 µg/L chlorophyll-a

Trending lakes

Improving

  1. 1.Charles Mill Reservoir — Ashland County
  2. 2.Sites Lake — Richland County
  3. 3.Maumee Bay Off Maumee Bay State Park Lake — Lucas County

Declining

  1. 1.Caesar Creek Lake — Warren County
  2. 2.Maumee Bay Off Woodtick Peninsula Lake — Lucas County
  3. 3.Tappan Lake @ Cadiz Public Water Supply Intake — Harrison County

Impaired waters in Ohio

14 lakes appear on the EPA/state 303(d) impaired-waters list (12 formally listed, 11 with a cleanup plan/TMDL).

Pathogens (E. coli, fecal) · 10Sediment / turbidity · 9Nutrients (phosphorus, nitrogen) · 9Habitat alterations · 8Oxygen depletion (low DO) · 7Algal growth · 5Hydrologic alteration · 5Metals (other than mercury) · 4

Explore Ohio lakes

Lake Fishing Forecast

Species activity outlook by water temperature and season

Ohio Lake Trips

Where to stay at Ohio's top lakes, each with its readings

Lakes near Columbus

Cleanest lakes within 50 miles of Columbus

Lakes near Cleveland

Cleanest lakes within 50 miles of Cleveland

Readings combine total phosphorus, total nitrogen, chlorophyll-a, and turbidity 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”.