What is the cleanest lake in Big Horn County, Montana?

Arapooish Pond in Big Horn County is the highest-rated lake in Big Horn County, Montana with an EPA water quality grade of NR.

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 Big Horn County, Montana

Arapooish Pond in Big Horn County leads the rankings with a water quality grade of NR. Below are the top 3 cleanest monitored lakes in Big Horn County, Montana, ranked by EPA water quality score.

Ranked List

#	Lake	County	Grade	Clarity	Phosphorus	Algae
1	Arapooish Pond	Big Horn	NR	-	-	-
2	Lodge Grass Storage Reservoir	Big Horn	NR	-	-	-
3	Tongue River Reservoir	Big Horn	NR	-	-	-

Ranked List

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