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

Updated August 2026

The State of Wyoming's Lakes 2026

Of 164 lakes in Wyoming, 78.1% earn a water-quality grade of A or B and 15.6% score D or F (average grade B). Boysen Reservoir Transitional Embayment is the cleanest; 6 lakes (3.7%) are on an official impaired-waters list.

Data Report

164
Monitored lakes graded
B
Average grade
78.1%
Grade A or B
3.7%
On impaired list

Wyoming grade distribution

B
C
D
A: 0 (0.0%)B: 50 (78.1%)C: 4 (6.3%)D: 10 (15.6%)F: 0 (0.0%)

Cleanest lakes in Wyoming

Highest combined water-quality score, 2026.

  1. 1.BBoysen Reservoir Transitional Embayment — Fremont County11.0 ft clarity · 10 µg/L P
  2. 2.DBrooks Lake — Fremont County6.3 ft clarity · 50 µg/L P

Most-polluted lakes

Lowest combined water-quality score among monitored lakes.

  1. 1.DBrooks Lake — Fremont County6.3 ft clarity · 50 µg/L P
  2. 2.BBoysen Reservoir Transitional Embayment — Fremont County11.0 ft clarity · 10 µg/L P

Worst algae hotspots

Highest measured chlorophyll-a (algae) concentration.

No qualifying lakes with sufficient data.

Trending lakes

Improving

  1. 1.BAlcova Reservoir Transitional Pelagic — Natrona County
  2. 2.BGlendo Reservoir Riverine Pelagic — Platte County
  3. 3.BSeminoe Reservoir Lacustrine Pelagic — Carbon County
  4. 4.BAlcova Reservoir Riverine Pelagic — Natrona County
  5. 5.BCrystal Reservoir — Laramie County
  6. 6.BGranite Springs Reservoir — Laramie County
  7. 7.BLake Desmet Lpd — Johnson County
  8. 8.BRob Roy Reservoir — Albany County

Declining

  1. 1.DHawk Springs Reservoir — Goshen County
  2. 2.DFesto Lake — Platte County
  3. 3.DBrooks Lake — Fremont County
  4. 4.CUnnamed Reservoir — Big Horn County
  5. 5.BSeminoe Reservoir Riverine Pelagic — Carbon County
  6. 6.BGlendo Reservoir Lacustrine Pelagic — Platte County
  7. 7.BSeminoe Reservoir Transitional Pelagic — Carbon County
  8. 8.BLake Hattie — Albany County

Impaired waters in Wyoming

6 lakes appear on the EPA/state 303(d) impaired-waters list (5 formally listed, 1 with a cleanup plan/TMDL).

Nutrients (phosphorus, nitrogen) · 5pH / acidity · 5Sediment / turbidity · 1

Explore Wyoming lakes

Lake Fishing Forecast

Species activity outlook by water temperature and season

Wyoming Lake Trips

Where to stay at Wyoming'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 Wyoming lakes.

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