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

Updated August 2026

The State of Tennessee's Lakes 2026

Of 67 lakes in Tennessee, 3.6% earn a water-quality grade of A or B and 67.9% score D or F (average grade D). Piney River Lake is the cleanest; 22 lakes (32.8%) are on an official impaired-waters list.

Data Report

67
Monitored lakes graded
D
Average grade
3.6%
Grade A or B
32.8%
On impaired list

Tennessee grade distribution

C
D
A: 0 (0.0%)B: 1 (3.6%)C: 8 (28.6%)D: 19 (67.9%)F: 0 (0.0%)

Cleanest lakes in Tennessee

Highest combined water-quality score, 2026.

  1. 1.BPiney River Lake — Rhea County6.4 ft clarity · 18 µg/L P
  2. 2.CHiwassee River Lake — Bradley County4.1 ft clarity · 29 µg/L P
  3. 3.CTennessee River Lake — Rhea County7.1 ft clarity · 29 µg/L P
  4. 4.CTennessee River Lake — Knox County33 µg/L P
  5. 5.CTennessee River Lake — Roane County29 µg/L P
  6. 6.DTennessee River Lake — Marion County7.6 ft clarity · 35 µg/L P
  7. 7.DTennessee River Lake — Henry County57 µg/L P
  8. 8.DOcoee River Lake — Polk County7.5 ft clarity · 50 µg/L P
  9. 9.DClinch River Lake — Roane County36 µg/L P
  10. 10.DCumberland River Lake — Davidson County69 µg/L P

Most-polluted lakes

Lowest combined water-quality score among monitored lakes.

  1. 1.DTennessee River Lake — Marion County7.6 ft clarity · 35 µg/L P
  2. 2.DTennessee River Lake — Henry County57 µg/L P
  3. 3.DOcoee River Lake — Polk County7.5 ft clarity · 50 µg/L P
  4. 4.DClinch River Lake — Roane County36 µg/L P
  5. 5.DCumberland River Lake — Davidson County69 µg/L P
  6. 6.DCumberland River Lake — Wilson County35 µg/L P
  7. 7.DBig Sandy River Lake — Benton County64 µg/L P
  8. 8.DBeech River Lake — Decatur County96 µg/L P
  9. 9.DDuck River Lake — Humphreys County200 µg/L P
  10. 10.DRobertson Creek Lake — Hawkins County48 µg/L P

Worst algae hotspots

Highest measured chlorophyll-a (algae) concentration.

No qualifying lakes with sufficient data.

Trending lakes

Improving

  1. 1.BPiney River Lake — Rhea County
  2. 2.CTennessee River Lake — Knox County
  3. 3.CTennessee River Lake — Roane County
  4. 4.CPoor Valley Creek Lake — Hawkins County
  5. 5.CEmory River Lake — Roane County
  6. 6.DOcoee River Lake — Polk County
  7. 7.DReelfoot Lake Blue Basin — Lake County
  8. 8.DMckellar Lake — Shelby County

Declining

  1. 1.DTennessee River Lake — Marion County
  2. 2.DCumberland River Lake — Wilson County
  3. 3.DCumberland River Lake — Stewart County
  4. 4.DBig Sandy River Lake — Benton County
  5. 5.CCalderwood Lake — Blount County
  6. 6.NRStock Creek Lake — Hawkins County
  7. 7.NRDrakes Creek Lake — Sumner County

Impaired waters in Tennessee

22 lakes appear on the EPA/state 303(d) impaired-waters list (21 formally listed, 7 with a cleanup plan/TMDL).

PCBs · 12Mercury · 11Sediment / turbidity · 9Nutrients (phosphorus, nitrogen) · 7Oxygen depletion (low DO) · 7Pathogens (E. coli, fecal) · 6Pesticides · 5Dioxins · 4

Explore Tennessee lakes

Lake Fishing Forecast

Species activity outlook by water temperature and season

Tennessee Lake Trips

Where to stay at Tennessee's top lakes, each with its grade

Grades 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 Tennessee lakes.

Cite this report: LakeQuality, “The State of Tennessee's Lakes 2026”.