Gem County Lake Quality
Idaho, 2 lakes, average grade A (Excellent)
Only 2 lakes in Gem 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. On average, Gem County lakes grade an A. That puts it near the top of the {{stateName}} county ranking.
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 Nla Lake (A); the most-stressed is Black Cnyn Reservoir Ns of (B).
Quick Answers for Gem County
Planning a trip? Check special fishing regulations for Nla Lake — or check the official Idaho fishing regulations.
All Lakes in Gem County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Nla Lake | A | 17.6 ft | 19.7 µg/L |
| 2 | Black Cnyn Reservoir Ns of | B | 7.5 ft | 29.5 µg/L |
Other Counties in Idaho
See how Gem 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 Gem County
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Source: EPA National Aquatic Resource Surveys, 2026.