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LakeQuality

Data Report · Updated July 2026

The State of Oregon’s Lakes 2026

Of 73 monitored lakes in Oregon, 54.8% earn a water-quality grade of A or B and 35.6% score D or F (average grade C). Odell Lake is the cleanest;

73
Monitored lakes graded
C
Average grade
54.8%
Grade A or B
0%
On impaired list

Oregon grade distribution

A
B
C
F
A: 24 (32.9%)B: 16 (21.9%)C: 7 (9.6%)D: 4 (5.5%)F: 22 (30.1%)

Cleanest lakes in Oregon

Highest combined water-quality score, 2026.

  1. 1.AOdell Lake — Klamath County22.3 ft clarity · 1 µg/L chl-a
  2. 2.ACrescent Lake — Klamath County42.2 ft clarity · 1 µg/L chl-a
  3. 3.AOdell Lake — Klamath County18.7 ft clarity · 1 µg/L chl-a
  4. 4.ACrescent Lake — Klamath County51.7 ft clarity · 1 µg/L chl-a
  5. 5.ALava Lake — Deschutes County17.6 ft clarity · 7 µg/L chl-a
  6. 6.AWickiup Reservoir — Deschutes County11.2 ft clarity · 3 µg/L chl-a
  7. 7.BBilly Chinook Reservoir — Jefferson County8.4 ft clarity · 2 µg/L chl-a
  8. 8.BCrane Prairie Reservoir — Deschutes County8.4 ft clarity · 4 µg/L chl-a
  9. 9.BCrane Prairie Reservoir — Deschutes County12.5 ft clarity · 5 µg/L chl-a
  10. 10.BDeschutes River Arm Lake — Jefferson County4.6 ft clarity · 4 µg/L chl-a

Most-polluted lakes

Lowest combined water-quality score among monitored lakes.

  1. 1.FMckay Lake — Umatilla County3.3 ft clarity · 122 µg/L P
  2. 2.FHoward Prairie Reservoir — Jackson County2.3 ft clarity · 124 µg/L P
  3. 3.FWilliamson River Outlet Lake — Klamath County165 µg/L P · 71 µg/L chl-a
  4. 4.FMalheur Lake — Harney County808 µg/L P · 46 µg/L chl-a
  5. 5.FMid-Trench Lake — Klamath County240 µg/L P · 81 µg/L chl-a
  6. 6.FAgency Lake South — Klamath County110 µg/L P · 62 µg/L chl-a
  7. 7.FShoalwater Bay Lake — Klamath County220 µg/L P · 147 µg/L chl-a
  8. 8.FUpper Klamath Lake — Klamath County195 µg/L P · 117 µg/L chl-a
  9. 9.FRattlesnake Point Lake — Klamath County185 µg/L P · 125 µg/L chl-a
  10. 10.FMid-North Lake — Klamath County180 µg/L P · 83 µg/L chl-a

Worst algae hotspots

Highest measured chlorophyll-a (algae) concentration.

  1. 1.FBrownlee Reservoir — Baker County198 µg/L chlorophyll-a
  2. 2.FShoalwater Bay Lake — Klamath County147 µg/L chlorophyll-a
  3. 3.FCold Springs Reservoir — Umatilla County126 µg/L chlorophyll-a
  4. 4.FRattlesnake Point Lake — Klamath County125 µg/L chlorophyll-a
  5. 5.FUpper Klamath Lake — Klamath County117 µg/L chlorophyll-a
  6. 6.FLake Billy Chinook — Jefferson County94 µg/L chlorophyll-a
  7. 7.FMid-North Lake — Klamath County83 µg/L chlorophyll-a
  8. 8.FMid-Trench Lake — Klamath County81 µg/L chlorophyll-a
  9. 9.FUpper Klamath Lake — Klamath County72 µg/L chlorophyll-a
  10. 10.FWilliamson River Outlet Lake — Klamath County71 µg/L chlorophyll-a

Explore Oregon 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 Oregon lakes.

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