Big Horn County Lake Quality
Montana, 7 lakes, average grade B (Good)
Big Horn County has 7 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, Big Horn County sits comfortably above the {{stateName}} median.
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. Bighorn Lake (C) is the cleanest in the county.
Quick Answers for Big Horn County
Planning a trip? Check special fishing regulations for Bighorn Lake — or check the official Montana fishing regulations.
All Lakes in Big Horn County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Bighorn Lake | C | - | 37 µg/L |
| 2 | Nla Lake | D | 4.9 ft | 82000 µg/L |
Other Counties in Montana
See how Big Horn 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 Big Horn County
Top-rated places to stay near Big Horn County
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Source: EPA National Aquatic Resource Surveys, 2026.