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The State of Idaho's Lakes

Idaho's cleanest lakes, ranked on agency measurements

Lake Fishing Forecast

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Idaho Lake Trips

Where to stay at Idaho's top lakes, each with its readings

Reservoirs in Idaho

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12 of 301 Idaho lakes (4%) are man-made reservoirs in the USACE National Inventory of Dams. 12 carry a High or Significant hazard rating. The oldest matched dam dates to 1906.

Irrigation (6)Flood Risk Reduction (3)Hydroelectric (2)Fish and Wildlife Pond (1)

EPA-Impaired Lakes in Idaho

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40 of 301 Idaho lakes (13%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 24 have an approved Total Maximum Daily Load (TMDL) restoration plan.

Nutrients (phosphorus, nitrogen) (19)Mercury (16)Metals (other than mercury) (8)Hydrologic alteration (6)Oxygen depletion (low DO) (5)Sediment / turbidity (5)Turbidity (3)Temperature (3)

Idaho Fishing & Recreation

Licenses, regulations, records, and where to fish across Idaho.

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Counties

All 41 Idaho counties, ranked by average lake water quality. Compare them against every county nationwide in the county rankings, browse the full directory of lakes, or pick a different state.

Cleanest Idaho Lakes

15 lakes15 lakes ranked on readings

#	Lake	County	Clarity	Trophic	Max Depth	Access
1	Black Cnyn Reservoir Ns of	Gem	7.5 ft	Mesotrophic	No recent samples	✓ Public
2	Deadwood Reservoir	Valley	17.2 ft	Oligotrophic	No recent samples	Not recorded
3	Lake Lowell Across From Upper Embankment	Canyon	7.2 ft	Mesotrophic	No recent samples	✓ Public
4	Pasisades Reservoir	Bonneville	10.5 ft	Mesotrophic	No recent samples	✓ Public
5	Palisades Lake	Bonneville	13.1 ft	Mesotrophic	No recent samples	Not recorded
6	Palisades Reservoir	Bonneville	12.5 ft	Oligotrophic	No recent samples	✓ Public
7	Mud Lake	Bear Lake	No recent samples	Eutrophic	No recent samples	Not recorded
8	Cas Reservoir Inlet Between Lf And	Valley	4.3 ft	Eutrophic	No recent samples	✓ Public
9	Lake Walcott	Cassia	4.3 ft	Eutrophic	No recent samples	✓ Public
10	Island Park Lake	Fremont	9.8 ft	Eutrophic	No recent samples	✓ Public
11	Cascade R W of Sugarloaf Island Lake	Valley	8.2 ft	Eutrophic	No recent samples	✓ Public
12	Island Pk Reservoir	Fremont	2.3 ft	Eutrophic	No recent samples	Not recorded
13	Littlewood Lake	Blaine	12.5 ft	Eutrophic	No recent samples	✓ Public
14	Mountain View Lake	Owyhee	No recent samples	Eutrophic	No recent samples	✓ Public
15	American Falls R-Little Hole Draw Lake	Power	No recent samples	Eutrophic	No recent samples	Not recorded

Idaho lists 301 lakes across 41 counties, 27 of them with a recent water-quality reading. Most of that sampling flows through monitoring run by the Idaho Department of Environmental Quality, which feeds state, federal, and volunteer measurements into the EPA Water Quality Portal. The remainder are here because they are real named lakes, not because anyone has sampled them recently.

Lake Pend Oreille is the largest lake in this index at about 92,764 acres, one of 46 here that clear 500 acres. The rest run smaller, and small and shallow is where nutrient loading shows up first, because there is less water to dilute it and the bottom sediment stays within reach of the sun. Gem has the lowest nutrient and algae readings on average. With only 41 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.

Lake Match

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Source: EPA National Aquatic Resource Surveys and the EPA Water Quality Portal.

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