
Granite County Lake Quality
Montana, 10 lakes — no lake here has enough monitoring data for a grade
Granite County holds 10 monitored lakes. With a sample that small the county-level summary describes those specific waters, not necessarily every water body in the county. No lake in Granite County has enough sampling behind it for an A–F grade yet. The 10 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 Granite County
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Quick Answers for Granite County
Planning a trip? Check special fishing regulations for Johnson Lake — or check the official Montana fishing regulations.
All Lakes in Granite County
10 lakes · 0 graded, 10 not rated0 graded lakes · 10 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| NRJohnson LakeGranite | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRCarpp LakeGranite | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRMedicine LakeGranite | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NREcho LakeGranite | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRRacetrack LakeGranite | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRFred Burr LakeGranite | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRFisher LakeGranite | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRBig Pozega LakeGranite | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRThornton LakeGranite | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRLower Willow Creek ReservoirGranite | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not 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.
Lake Match
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Other Counties in Montana
See how Granite 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.