Updated Jul 2026
Idaho Lake Water Quality
Water quality grades for 96 monitored lakes across 33 counties.
96 {{stateName}} lakes carry a grade. Most of the input data flows through monitoring run by {{agency}}, which feeds state, federal, and volunteer measurements into the EPA Water Quality Portal. About 24% of graded {{stateName}} lakes earn an A. The bulk sit in the middle B–C range; 21% fall into D or F, almost all of those in counties where row-crop agriculture dominates the watershed.
Eutrophic conditions dominate — nutrient-loaded, productive, with algal pressure that shows up most years in late summer. These lakes tend to be shallow, agricultural-watershed, and over-warmed by the time July ends. Kootenai ranks highest on average county grade (A). Camas sits lowest. With only 33 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.
Grade Distribution
How Idaho’s 96 graded lakes break down from A (excellent) to F.
Top-Graded Idaho Lakes
The highest water-quality grades in Idaho — clarity, depth, and A-F grade at a glance.
Nla Lake
Gem County, Idaho
See grade for Nla Lake →Nla Lake
Valley County, Idaho
See grade for Nla Lake →Nla Lake
Blaine County, Idaho
See grade for Nla Lake →Nla Lake
Kootenai County, Idaho
See grade for Nla Lake →Nla Lake
Shoshone County, Idaho
See grade for Nla Lake →Nla Lake
Valley County, Idaho
See grade for Nla Lake →Nla Lake
Custer County, Idaho
See grade for Nla Lake →Deadwood Reservoir
Valley County, Idaho
See grade for Deadwood Reservoir →Ririe Reservoir
Bonneville County, Idaho
See grade for Ririe Reservoir →Lake Map
Explore Idaho Lakes
Idaho reports, fishing & travel
Idaho Fishing & Recreation
Licenses, regulations, records, and where to fish across Idaho.
Counties
All 33 Idaho counties, ranked by average lake water quality. Compare them against every county nationwide in the county rankings, browse the full directory of graded lakes, or pick a different state.
Top 25 Cleanest Lakes
| Rank | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | Nla Lake | Gem | A | 17.6 ft |
| 2 | Nla Lake | Valley | A | 18.6 ft |
| 3 | Nla Lake | Blaine | A | 29.9 ft |
| 4 | Nla Lake | Kootenai | A | 19.2 ft |
| 5 | Nla Lake | Shoshone | A | - |
| 6 | Nla Lake | Valley | A | - |
| 7 | Nla Lake | Custer | A | - |
| 8 | Deadwood Reservoir | Valley | A | 17.2 ft |
| 9 | Ririe Reservoir | Bonneville | A | - |
| 10 | Bear Lake Off North Beach | Bear Lake | A | 21.7 ft |
| 11 | Bear Lake | Bear Lake | A | 19 ft |
| 12 | Bear Lake Se of St Charles Replicate of | Bear Lake | A | 19 ft |
| 13 | Usgs Lake | Kootenai | A | - |
| 14 | Ideq Lake | Kootenai | A | - |
| 15 | Ideq Lake | Kootenai | A | - |
| 16 | Ideq Lake | Kootenai | A | - |
| 17 | Coeur D' Alene Lake | Kootenai | A | - |
| 18 | Cat Creek Lake | Elmore | A | - |
| 19 | Cat Creek Reference Lake | Elmore | A | - |
| 20 | Nla Lake | Bonner | A | 11 ft |
| 21 | Pasisades Reservoir | Bonneville | A | 10.5 ft |
| 22 | Palisades Reservoir | Bonneville | A | 12.5 ft |
| 23 | Deadwood Res Off Face of Dam Lake | Valley | A | - |
| 24 | Nla Lake | Bonner | B | 6.9 ft |
| 25 | Palisades Lake | Bonneville | B | 13.1 ft |
25 Lakes Needing Attention
| Rank | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | Mpipeline Rd Lake | Owyhee | F | - |
| 2 | Nla Lake | Owyhee | F | 0.7 ft |
| 3 | Nla Lake | Camas | F | 0.8 ft |
| 4 | Nla Lake | Camas | F | 5.2 ft |
| 5 | Nla Lake | Bear Lake | F | 3.3 ft |
| 6 | Little Wood Reservoir | Blaine | D | - |
| 7 | Nla Lake | Elmore | D | 3.4 ft |
| 8 | Nla Lake | Fremont | D | 3.4 ft |
| 9 | Nla Lake | Owyhee | D | 0.7 ft |
| 10 | Nla Lake | Latah | D | 3.4 ft |
| 11 | Mann Creek Reservoir | Washington | D | - |
| 12 | Nla Lake | Fremont | D | 6.2 ft |
| 13 | Nla Lake | Owyhee | D | 5.2 ft |
| 14 | Nla Lake | Idaho | D | 2 ft |
| 15 | Nla Lake | Twin Falls | D | 5.6 ft |
| 16 | Nla Lake | Franklin | D | 5.2 ft |
| 17 | Ririe Lake | Bonneville | D | 4.6 ft |
| 18 | Nla Lake | Owyhee | D | 3 ft |
| 19 | Nla Lake | Ada | D | 1.3 ft |
| 20 | Nla Lake | Bonner | D | 6.5 ft |
| 21 | American Falls R-Little Hole Draw Lake | Power | C | - |
| 22 | American Falls R-Sportsmans Cove Lake | Power | C | - |
| 23 | Island Pk Reservoir | Fremont | C | 2.3 ft |
| 24 | Lake Walcott | Cassia | C | 4.3 ft |
| 25 | Cas Reservoir Inlet Between Lf And | Valley | C | 4.3 ft |
Where to stay near Idaho
Top-rated places to stay near Idaho
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Source: EPA National Aquatic Resource Surveys, 2026.