Carbon County Lake Quality
Montana, 8 lakes, average grade B (Good)
Carbon County has 8 graded lakes — a thin enough sample that one or two stressed lakes can move the county average noticeably. Use the per-lake pages below for what actually matters. With an average grade of B, Carbon 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 Cooney Reservoir (A); the most-stressed is Nla Lake (B).
Quick Answers for Carbon County
Planning a trip? Check special fishing regulations for Cooney Reservoir — or check the official Montana fishing regulations.
All Lakes in Carbon County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Cooney Reservoir | A | 12.5 ft | 19.5 µg/L |
| 2 | Cooney Reservoir | B | 9.3 ft | 15 µg/L |
| 3 | Cooney Reservoir | B | 8.1 ft | 16 µg/L |
| 4 | Nla Lake | B | 18.5 ft | 8000 µg/L |
Other Counties in Montana
See how Carbon 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 Carbon County
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Source: EPA National Aquatic Resource Surveys, 2026.