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Late afternoon sun over Slim Lake, scattering a bright path across wind-textured water
NR

Rosebud County Lake Quality

Montana, 15 lakes — no lake here has enough monitoring data for a grade

There are 15 monitored lakes in Rosebud County. The mix is varied enough that the county-level average tells you the broad strokes, not the choose-this-cabin specifics. No lake in Rosebud County has enough sampling behind it for an A–F grade yet. The 15 monitored lakes below carry whatever clarity, phosphorus, and chlorophyll-a measurements exist.

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.

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Top-rated places to stay near Rosebud County

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All Lakes in Rosebud County

15 lakes · 0 graded, 15 not rated0 graded lakes · 15 not rated, hidden

#LakeGradeClarityPhosphorusAlgaeTrophicAccess
NRCastle Rock LakeRosebudNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRStellar LakeRosebudNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRBoies ReservoirRosebudNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRBarley ReservoirRosebudNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRBarley ReservoirsRosebudNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRBrown Coulee ReservoirRosebudNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRKerns ReservoirRosebudNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRBlacktail ReservoirRosebudNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRBlacktail ReservoirRosebudNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRZempel LakeRosebudNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRZempel LakeRosebudNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRDonleys ReservoirRosebudNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRThebes LakeRosebudNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRBlack Sea ReservoirRosebudNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRBlack Sea ReservoirRosebudNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded

NR = not rated: there is not enough recent sampling to support a letter. That is EPA Integrated Reporting Category 3 (insufficient information), not a failing grade. How grading works.

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See how Rosebud County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all United States (49 states), Canada (Ontario, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador), and 38 other country hubs..

Source: EPA National Aquatic Resource Surveys, 2026.