What is the cleanest lake in Idaho?

Mann Creek Reservoir in Washington County has the cleanest nutrient and algae readings in Idaho.

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.

Lakes With Algae Readings in Idaho

4 lakes in Idaho report elevated algae levels (chlorophyll-a above 20 µg/L). These lakes are most likely to develop blue-green algae blooms during warm, calm summer weather. Avoid swimming during visible blooms and rinse pets after contact.

Ranked List

#	Lake	County	Clarity	Phosphorus	Algae
1	Mann Creek Reservoir	Washington	-	49 µg/L	179 µg/L
2	Little Wood Reservoir	Blaine	-	70 µg/L	30.2 µg/L
3	Soldier Meadow Reservoir East Arm	Nez Perce	4.6 ft	34 µg/L	29 µg/L
4	Soldiers Meadow Reservoir West Arm	Nez Perce	3.6 ft	56.5 µg/L	28.5 µg/L

Ranked List

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