Rosebud County Lake Quality
Montana, 2 lakes, average grade B (Good)
Only 2 lakes in Rosebud 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-wide average lands at B — solid water quality with most lakes carrying clear summer transparency and low-to-moderate phosphorus.
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. Castle Rock Lake (A) is the cleanest in the county.
Quick Answers for Rosebud County
Planning a trip? Check special fishing regulations for Castle Rock Lake — or check the official Montana fishing regulations.
All Lakes in Rosebud County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Castle Rock Lake | A | - | 1 µg/L |
| 2 | Nla Lake | D | 4.9 ft | 94.7 µg/L |
Other Counties in Montana
See how Rosebud 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 Rosebud County
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Source: EPA National Aquatic Resource Surveys, 2026.