What is the cleanest lake in Gem County, Idaho?

Black Cnyn Reservoir Ns of in Gem County is the highest-rated lake in Gem County, Idaho with an EPA water quality grade of A and 7.5 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 Gem County, Idaho

Black Cnyn Reservoir Ns of in Gem County leads the rankings with a water quality grade of A and 7.5 ft of clarity. Below are the top 2 cleanest monitored lakes in Gem County, Idaho, ranked by EPA water quality score.

Ranked List

#	Lake	County	Grade	Clarity	Phosphorus	Algae
1	Black Cnyn Reservoir Ns of	Gem	A	7.5 ft	29.5 µg/L	3.1 µg/L
2	Black Canyon Reservoir	Gem	NR	-	-	-

Ranked List

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