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

Updated August 2026

The State of Arizona's Lakes 2026

Of 73 lakes in Arizona, 28.6% earn a water-quality grade of A or B and 28.6% score D or F (average grade C). Ak-Chin Reservoir is the cleanest; 19 lakes (26%) are on an official impaired-waters list.

Data Report

73
Monitored lakes graded
C
Average grade
28.6%
Grade A or B
26%
On impaired list

Arizona grade distribution

B
C
D
A: 0 (0.0%)B: 2 (28.6%)C: 3 (42.9%)D: 2 (28.6%)F: 0 (0.0%)

Cleanest lakes in Arizona

Highest combined water-quality score, 2026.

  1. 1.BAk-Chin Reservoir — Pinal County28 µg/L P · 4 µg/L chl-a
  2. 2.DSunris Park Lake — Yuma County99 µg/L P

Most-polluted lakes

Lowest combined water-quality score among monitored lakes.

  1. 1.DSunris Park Lake — Yuma County99 µg/L P
  2. 2.BAk-Chin Reservoir — Pinal County28 µg/L P · 4 µg/L chl-a

Worst algae hotspots

Highest measured chlorophyll-a (algae) concentration.

No qualifying lakes with sufficient data.

Trending lakes

Improving

  1. 1.BChaparral Park Lake — Maricopa County
  2. 2.BAk-Chin Reservoir — Pinal County
  3. 3.CLakeside Lake — Pima County
  4. 4.NRWoods Canyon Lake — Coconino County
  5. 5.NRWillow Creek Reservoir — Yavapai County
  6. 6.NRLynx Lake — Yavapai County
  7. 7.NRShow Low Lake — Navajo County
  8. 8.NRAshurst Lake — Coconino County

Declining

  1. 1.DSunris Park Lake — Yuma County
  2. 2.CCanyon Lake — Maricopa County
  3. 3.CRose Canyon Lake — Pima County
  4. 4.NRTempe Town Lake — Maricopa County
  5. 5.NRSaguaro Lake — Maricopa County
  6. 6.NRPena Blanca Lake — Santa Cruz County
  7. 7.NRWhitehorse Lake — Coconino County
  8. 8.NRFool Hollow Lake — Navajo County

Impaired waters in Arizona

19 lakes appear on the EPA/state 303(d) impaired-waters list (13 formally listed, 7 with a cleanup plan/TMDL).

Mercury · 12Oxygen depletion (low DO) · 6pH / acidity · 6Nutrients (phosphorus, nitrogen) · 5Ammonia · 2Noxious aquatic plants · 1Metals (other than mercury) · 1

Explore Arizona lakes

Lake Fishing Forecast

Species activity outlook by water temperature and season

Arizona Lake Trips

Where to stay at Arizona'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 Arizona lakes.

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