What is the cleanest lake in Union County, Iowa?

Three Mile Lake in Union County is the highest-rated lake in Union County, Iowa with an EPA water quality grade of D and 2.7 feet of water clarity.

How are these rankings calculated?

Lakes are graded A through F on nutrients and algae — total phosphorus, nitrogen, chlorophyll-a, and turbidity — against EPA National Lakes Assessment 2022 condition classes for that lake’s ecoregion. Water clarity (Secchi depth) is measured and shown; it is not the letter. Lakes without enough recent samples are UNRATED, not given an F. Source data comes from the EPA Water Quality Portal.

Cleanest Lakes in Union County, Iowa

Three Mile Lake in Union County leads the rankings with a water quality grade of D and 2.7 ft of clarity. Below are the top 6 cleanest monitored lakes in Union County, Iowa, ranked by EPA water quality score.

Ranked List

#	Lake	County	Grade	Clarity	Phosphorus	Algae
1	Three Mile Lake	Union	D	2.7 ft	43 µg/L	28.4 µg/L
2	Twelve Mile Lake	Union	F	2.4 ft	79 µg/L	45 µg/L
3	Green Valley Lake	Union	F	1.5 ft	103 µg/L	61.7 µg/L
4	Summit Lake	Union	F	1.4 ft	121 µg/L	45.7 µg/L
5	Mckinley Lake	Union	F	1 ft	150 µg/L	69.3 µg/L
6	Thayer Lake	Union	F	3.5 ft	68 µg/L	34.3 µg/L

Ranked List

More Answers for Union County, Iowa