Elmore County Lake Quality
Idaho, 8 lakes, average grade B (Good)
Only 8 lakes in Elmore County carry an active grade. The county-level summary is therefore representative of those specific lakes, not necessarily of every water body in the county. With an average grade of B, Elmore County sits comfortably above the {{stateName}} median.
The county's lakes lean shallow, which makes the grades sensitive to wind, sediment-resuspension, and any nutrient inputs from the watershed. The cleanest lake on the books is Cat Creek Lake (A); the most-stressed is Nla Lake (D).
Quick Answers for Elmore County
Planning a trip? Check special fishing regulations for Cat Creek Lake — or check the official Idaho fishing regulations.
All Lakes in Elmore County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Cat Creek Lake | A | - | 17 µg/L |
| 2 | Cat Creek Reference Lake | A | - | - |
| 3 | Arrowrock Reservoir | B | 12.5 ft | 35 µg/L |
| 4 | Arrowrock Reservoir | C | 9.5 ft | 55.5 µg/L |
| 5 | Nla Lake | D | 3.4 ft | 93000 µg/L |
Other Counties in Idaho
See how Elmore County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 34 states.
Where to stay near Elmore County
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Source: EPA National Aquatic Resource Surveys, 2026.