Beaverhead County Lake Quality
Montana, 5 lakes, average grade C (Fair)
Only 5 lakes in Beaverhead 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.
Most of the county's monitored lakes are shallow — under 50 feet — which means wind keeps the water column mixed all summer and sediment-bound phosphorus releases back into the surface layer whenever the bottom is disturbed. Nla Lake (A) is the cleanest in the county.
Quick Answers for Beaverhead County
Planning a trip? Check special fishing regulations for Nla Lake — or check the official Montana fishing regulations.
All Lakes in Beaverhead County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Nla Lake | A | 13.1 ft | 15.4 µg/L |
| 2 | Nla Lake | B | 24.6 ft | 11000 µg/L |
| 3 | Clark Canyon Reservoir | C | 7.4 ft | 30 µg/L |
| 4 | Nla Lake | C | 2.6 ft | 56 µg/L |
| 5 | Clark Canyon Reservoir South of Island | D | 4.9 ft | - |
Other Counties in Montana
See how Beaverhead 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.