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 · 20 µg/L P · 2 µg/L chl-a
2. 2.ADale Maffitt Reservoir — Dallas County9.8 ft clarity · 20 µg/L P · 2 µg/L chl-a
3. 3.ABlue Pit Lake — Cerro Gordo County17.1 ft clarity · 20 µg/L P · 2 µg/L chl-a
4. 4.AAda Hayden Heritage Park Lake — Story County6.8 ft clarity · 19 µg/L P · 5 µg/L chl-a
5. 5.ALittle Sioux Park Lake — Woodbury County5.7 ft clarity · 19 µg/L P · 6 µg/L chl-a
6. 6.ARudd Lake — Floyd County8.1 ft clarity · 14 µg/L P · 5 µg/L chl-a
7. 7.ASlipbluff Lake — Decatur County9.0 ft clarity · 18 µg/L P · 5 µg/L chl-a
8. 8.ALacey Keosauqua Lake — Van Buren County7.1 ft clarity · 22 µg/L P · 5 µg/L chl-a
9. 9.AYenruogis Pond — Keokuk County9.9 ft clarity · 21 µg/L P · 6 µg/L chl-a
10. 10.ASand Lake — Marshall County6.4 ft clarity · 25 µg/L P · 4 µg/L chl-a

Most-polluted lakes

Lowest combined water-quality score among monitored lakes.

1. 1.FBig Creek Lake — Polk County2.6 ft clarity · 80 µg/L P · 36 µg/L chl-a
2. 2.FArrowhead Lake — Pottawattamie County1.8 ft clarity · 136 µg/L P · 54 µg/L chl-a
3. 3.FWhite Oak Lake — Mahaska County1.4 ft clarity · 126 µg/L P · 69 µg/L chl-a
4. 4.FCrystal Lake Max Depth — Hancock County1.6 ft clarity · 99 µg/L P · 50 µg/L chl-a
5. 5.FHannen Lake — Benton County1.2 ft clarity · 141 µg/L P · 120 µg/L chl-a
6. 6.FBriggs Woods Lake — Hamilton County1.5 ft clarity · 87 µg/L P · 59 µg/L chl-a
7. 7.FNelson Lake — Crawford County3.8 ft clarity · 124 µg/L P · 31 µg/L chl-a
8. 8.FGrays Lake — Polk County1.6 ft clarity · 103 µg/L P · 47 µg/L chl-a
9. 9.FUnion Grove Lake — Tama County1.6 ft clarity · 144 µg/L P · 89 µg/L chl-a
10. 10.FCasey Lake — Tama County1.2 ft clarity · 113 µg/L P · 96 µg/L chl-a

Worst algae hotspots

Highest measured chlorophyll-a (algae) concentration.

1. 1.FCedar Lake — Linn County125 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.FRock Creek Max Depth Lake — Jasper County108 µg/L chlorophyll-a
5. 5.FLittlefield Lake — Audubon County103 µg/L chlorophyll-a
6. 6.FAlice Wyth Lake — Black Hawk County102 µg/L chlorophyll-a
7. 7.FLake Hendricks — Howard County99 µg/L chlorophyll-a
8. 8.FCasey Lake — Tama County96 µg/L chlorophyll-a
9. 9.FDesoto Bend Lake — Harrison County93 µg/L chlorophyll-a
10. 10.FLake Orient — Adair County92 µg/L chlorophyll-a

Trending lakes

Improving

1. 1.ADale Maffitt Reservoir — Dallas County
2. 2.ABlue Pit Lake — Cerro Gordo County
3. 3.ALacey Keosauqua Lake — Van Buren County
4. 4.AYenruogis Pond — Keokuk County
5. 5.BStorm Lake Max Depth — Buena Vista County
6. 6.BArrowhead Lake — Sac County
7. 7.BKent Park Lake — Johnson County
8. 8.BMormon Trail Lake — Adair County

Declining

1. 1.FWhite Oak Lake — Mahaska County
2. 2.FHannen Lake — Benton County
3. 3.FBriggs Woods Lake — Hamilton County
4. 4.FNelson Lake — Crawford County
5. 5.FGrays Lake — Polk County
6. 6.FLittlefield Lake — Audubon County
7. 7.FMeyers Lake — Black Hawk County
8. 8.FDiamond Lake — Poweshiek County