The State of Iowa’s Lakes 2026

Cleanest lakes in Iowa

Highest combined water-quality score, 2026.

1. 1.AWest Okoboji Lake — Dickinson County15.7 ft clarity · 3 µg/L chl-a
2. 2.ABlue Pit Lake — Cerro Gordo County17.1 ft clarity · 4 µg/L chl-a
3. 3.ANine Eagles Lake — Decatur County11.0 ft clarity · 3 µg/L chl-a
4. 4.ATerra Park Lake — Polk County11.5 ft clarity · 5 µg/L chl-a
5. 5.BDale Maffitt Reservoir — Dallas County9.8 ft clarity · 3 µg/L chl-a
6. 6.BRudd Lake — Floyd County8.1 ft clarity · 5 µg/L chl-a
7. 7.BSlipbluff Lake — Decatur County9.0 ft clarity · 5 µg/L chl-a
8. 8.BLacey Keosauqua Lake — Van Buren County7.1 ft clarity · 5 µg/L chl-a
9. 9.BYenruogis Pond — Keokuk County9.9 ft clarity · 6 µg/L chl-a
10. 10.BAda Hayden Heritage Park Lake — Story County6.8 ft clarity · 5 µg/L chl-a

Most-polluted lakes

Lowest combined water-quality score among monitored lakes.

1. 1.FWhite Oak Lake — Mahaska County1.4 ft clarity · 69 µg/L chl-a
2. 2.FBig Creek Lake — Polk County2.6 ft clarity · 36 µg/L chl-a
3. 3.FArrowhead Lake — Pottawattamie County1.8 ft clarity · 54 µg/L chl-a
4. 4.FCrystal Lake Max Depth — Hancock County1.6 ft clarity · 50 µg/L chl-a
5. 5.FHannen Lake — Benton County1.2 ft clarity · 120 µg/L chl-a
6. 6.FBriggs Woods Lake — Hamilton County1.5 ft clarity · 59 µg/L chl-a
7. 7.FGrays Lake — Polk County1.6 ft clarity · 47 µg/L chl-a
8. 8.FLittlefield Lake — Audubon County0.9 ft clarity · 103 µg/L chl-a
9. 9.FUnion Grove Lake — Tama County1.6 ft clarity · 89 µg/L chl-a
10. 10.FCasey Lake — Tama County1.2 ft clarity · 96 µg/L chl-a

Worst algae hotspots

Highest measured chlorophyll-a (algae) concentration.

1. 1.FCedar Lake — Linn County129 µg/L chlorophyll-a
2. 2.FHannen Lake — Benton County120 µg/L chlorophyll-a
3. 3.FMeyers Lake — Black Hawk County117 µg/L chlorophyll-a
4. 4.FLake Orient — Adair County110 µg/L chlorophyll-a
5. 5.FRock Creek Max Depth Lake — Jasper County108 µg/L chlorophyll-a
6. 6.FLittlefield Lake — Audubon County103 µg/L chlorophyll-a
7. 7.FAlice Wyth Lake — Black Hawk County102 µg/L chlorophyll-a
8. 8.FLake Hendricks — Howard County99 µg/L chlorophyll-a
9. 9.FCasey Lake — Tama County96 µg/L chlorophyll-a
10. 10.FDesoto Bend Lake — Harrison County93 µg/L chlorophyll-a

Trending lakes

Improving

1. 1.ABlue Pit Lake — Cerro Gordo County
2. 2.BDale Maffitt Reservoir — Dallas County
3. 3.BYenruogis Pond — Keokuk County
4. 4.BLambach Lake — Scott County
5. 5.CArrowhead Lake — Sac County
6. 6.CRailroad Lake — Scott County
7. 7.CMormon Trail Lake — Adair County
8. 8.CLake Wapello — Davis County

Declining

1. 1.FHannen Lake — Benton County
2. 2.FGrays Lake — Polk County
3. 3.FLittlefield Lake — Audubon County
4. 4.FMeyers Lake — Black Hawk County
5. 5.FBlue Heron Lake — Polk County
6. 6.FGreenfield Lake — Adair County
7. 7.FSilver Lake Max Depth — Delaware County
8. 8.FDon Williams Lake — Boone County