What is the cleanest lake in Idaho?

Black Cnyn Reservoir Ns of in Gem County has the cleanest nutrient and algae readings in Idaho, with 7.5 feet of measured water clarity.

How are these rankings calculated?

Nutrients and algae, total phosphorus, nitrogen, chlorophyll-a and turbidity, are read against EPA National Lakes Assessment 2022 condition classes for that lake’s ecoregion. Water clarity (Secchi depth) is measured and shown separately. Lakes without enough recent samples are listed without a condition class rather than ranked low. Source data comes from the EPA Water Quality Portal.

Best Lakes to Swim In in Idaho

1 lakes in Idaho lead the swimming list on clear, low-nutrient water with chlorophyll-a (algae) under 10 µg/L. Always check local advisories on the day you swim.

Ranked List

#	Lake	County	Clarity	Phosphorus	Algae
1	Black Cnyn Reservoir Ns of	Gem	7.5 ft	29.5 µg/L	3.1 µg/L

Ranked List

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