Fremont County Lake Quality
Idaho, 6 lakes, average grade C (Fair)
Only 6 lakes in Fremont 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. The county average is C — the middle of the rubric, with one or two lakes pulling the average up or down depending on year.
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 Island Park Lake (C); the most-stressed is Nla Lake (D).
Quick Answers for Fremont County
Planning a trip? Check special fishing regulations for Island Park Lake — or check the official Idaho fishing regulations.
All Lakes in Fremont County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Island Park Lake | C | 9.8 ft | 24 µg/L |
| 2 | Island Pk Reservoir | C | 2.3 ft | 56 µg/L |
| 3 | Nla Lake | D | 6.2 ft | 72 µg/L |
| 4 | Nla Lake | D | 3.4 ft | 79000 µg/L |
Other Counties in Idaho
See how Fremont County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 34 states.
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Source: EPA National Aquatic Resource Surveys, 2026.