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

Sheridan County Lake Quality

Montana, 23 lakes — no lake here has enough monitoring data for a grade

There are 23 monitored lakes in Sheridan 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 Sheridan County has enough sampling behind it for an A–F grade yet. The 23 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 Sheridan County

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All Lakes in Sheridan County

23 lakes · 0 graded, 23 not rated0 graded lakes · 23 not rated, hidden

#LakeGradeClarityPhosphorusAlgaeTrophicAccess
NRLochin SloughSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRSyme SloughSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRSalt LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRBrightsmen LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRPark LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRLone Tree LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRWidgeon SloughSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRLarson SloughSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRFlat LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRGaulke LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRNorth LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRGoose LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRTadpole LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRGoose LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRDominek LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRClear LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRBrush LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRLong LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRKaty LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRMedicine LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRHomestead LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRCapeneys LakeSheridanNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRBoxelder LakeSheridanNRNo 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 Sheridan 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.