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LakeQuality

Data Report · Updated July 2026

The State of Tennessee’s Lakes 2026

Of 82 monitored lakes in Tennessee, 19.5% earn a water-quality grade of A or B and 41.5% score D or F (average grade C). Nla Lake is the cleanest;

82
Monitored lakes graded
C
Average grade
19.5%
Grade A or B
0%
On impaired list

Tennessee grade distribution

A
B
C
D
F
A: 5 (6.1%)B: 11 (13.4%)C: 32 (39.0%)D: 17 (20.7%)F: 17 (20.7%)

Cleanest lakes in Tennessee

Highest combined water-quality score, 2026.

  1. 1.ANla Lake — Polk County5.4 ft clarity · 15 µg/L P · 1 µg/L chl-a
  2. 2.BNla Lake — Marion County6.7 ft clarity · 41 µg/L P · 3 µg/L chl-a
  3. 3.BNla Lake — Greene County2.5 ft clarity · 59 µg/L P · 1 µg/L chl-a
  4. 4.CNla Lake — Polk County16.4 ft clarity · 21000 µg/L P · 2 µg/L chl-a
  5. 5.CNla Lake — Stewart County4.1 ft clarity · 40 µg/L P · 14 µg/L chl-a
  6. 6.CNla Lake — Sullivan County10.3 ft clarity · 13000 µg/L P · 5 µg/L chl-a
  7. 7.CCumberland River Lake — Stewart County83 µg/L P · 13 µg/L chl-a
  8. 8.DNla Lake — Madison County3.4 ft clarity · 42000 µg/L P · 19 µg/L chl-a
  9. 9.DNla Lake — Hardeman County2.2 ft clarity · 48000 µg/L P · 19 µg/L chl-a
  10. 10.DNla Lake — McNairy County2.4 ft clarity · 43000 µg/L P · 19 µg/L chl-a

Most-polluted lakes

Lowest combined water-quality score among monitored lakes.

  1. 1.FNla Lake — Maury County1.5 ft clarity · 592 µg/L P · 50 µg/L chl-a
  2. 2.FNla Lake — Bedford County1.1 ft clarity · 589 µg/L P · 87 µg/L chl-a
  3. 3.FNla Lake — Shelby County2.0 ft clarity · 120000 µg/L P · 72 µg/L chl-a
  4. 4.FNla Lake — Marshall County2.1 ft clarity · 108 µg/L P · 60 µg/L chl-a
  5. 5.DNla Lake — Putnam County1.6 ft clarity · 179570 µg/L P · 29 µg/L chl-a
  6. 6.DNla Lake — Davidson County2.2 ft clarity · 25524 µg/L P · 27 µg/L chl-a
  7. 7.DNla Lake — Madison County3.4 ft clarity · 42000 µg/L P · 19 µg/L chl-a
  8. 8.DNla Lake — Hardeman County2.2 ft clarity · 48000 µg/L P · 19 µg/L chl-a
  9. 9.DNla Lake — McNairy County2.4 ft clarity · 43000 µg/L P · 19 µg/L chl-a
  10. 10.CNla Lake — Sullivan County10.3 ft clarity · 13000 µg/L P · 5 µg/L chl-a

Worst algae hotspots

Highest measured chlorophyll-a (algae) concentration.

  1. 1.FNla Lake — Bedford County87 µg/L chlorophyll-a
  2. 2.FNla Lake — Shelby County72 µg/L chlorophyll-a
  3. 3.FNla Lake — Marshall County60 µg/L chlorophyll-a
  4. 4.FNla Lake — Maury County50 µg/L chlorophyll-a
  5. 5.DNla Lake — Putnam County29 µg/L chlorophyll-a
  6. 6.DNla Lake — Davidson County27 µg/L chlorophyll-a

Explore Tennessee lakes

Lake Fishing Forecast

Species activity outlook by water temperature and season

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 Tennessee lakes.

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