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LakeQuality

Data Report · Updated July 2026

The State of Wyoming’s Lakes 2026

Of 243 monitored lakes in Wyoming, 45.7% earn a water-quality grade of A or B and 27.2% score D or F (average grade C). Flaming Gorge Reservoir is the cleanest;

243
Monitored lakes graded
C
Average grade
45.7%
Grade A or B
0%
On impaired list

Wyoming grade distribution

A
B
C
D
F
A: 41 (16.9%)B: 70 (28.8%)C: 66 (27.2%)D: 45 (18.5%)F: 21 (8.6%)

Cleanest lakes in Wyoming

Highest combined water-quality score, 2026.

  1. 1.AFlaming Gorge Reservoir — Sweetwater County22.0 ft clarity · 11 µg/L P · 1 µg/L chl-a
  2. 2.ANla Lake — Sublette County25.3 ft clarity · 8 µg/L P · 1 µg/L chl-a
  3. 3.AFlaming Gorge-Green River Lake — Sweetwater County18.4 ft clarity · 2 µg/L chl-a
  4. 4.AFontenelle Reservoir — Lincoln County15.0 ft clarity · 15 µg/L P
  5. 5.AFremont Lake — Sublette County42.8 ft clarity · 10 µg/L P
  6. 6.AWorthen Meadows Reservoir — Fremont County15.9 ft clarity · 10 µg/L P
  7. 7.AFlaming Gorge Res Bl Buckboard Replicate of Lake — Sweetwater County12.6 ft clarity · 7 µg/L P · 1 µg/L chl-a
  8. 8.AFontenelle Reservoir — Lincoln County13.3 ft clarity · 3 µg/L chl-a
  9. 9.AFontenelle Reservoir Lower-Mid — Lincoln County11.8 ft clarity · 4 µg/L chl-a
  10. 10.ASeminoe Reservoir Lacustrine Pelagic — Carbon County17.1 ft clarity · 25 µg/L P

Most-polluted lakes

Lowest combined water-quality score among monitored lakes.

  1. 1.FGlendo Reservoir Riverine Littoral — Platte County1.1 ft clarity · 130 µg/L P
  2. 2.FWoodruff Narrows Reservoir — Uinta County0.9 ft clarity · 92 µg/L P
  3. 3.FFesto Lake — Platte County0.8 ft clarity · 160 µg/L P
  4. 4.FHorseshoe Reservoir — Big Horn County1.8 ft clarity · 140 µg/L P
  5. 5.FGoshen Hole Reservoir — Goshen County1.1 ft clarity · 100 µg/L P
  6. 6.FBump-Sullivan Reservoir — Goshen County0.2 ft clarity · 420 µg/L P
  7. 7.FNla Lake — Teton County4.9 ft clarity · 34000 µg/L P · 35 µg/L chl-a
  8. 8.DGlendo Reservoir Riverine Pelagic — Platte County1.4 ft clarity · 60 µg/L P
  9. 9.DBig Sandy Reservoir Rtpd — Sublette County0.7 ft clarity · 60 µg/L P
  10. 10.DBuffalo Bill Reservoir Transitional Pelagic — Park County2.8 ft clarity · 70 µg/L P

Worst algae hotspots

Highest measured chlorophyll-a (algae) concentration.

  1. 1.FNla Lake — Teton County35 µg/L chlorophyll-a
  2. 2.DNla Lake — Park County28 µg/L chlorophyll-a
  3. 3.DNla Lake — Albany County20 µg/L chlorophyll-a

Explore Wyoming 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 Wyoming lakes.

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