Cleanest Lakes in Montana
Big Sky Lake South Hole in Missoula County leads the rankings with a water quality grade of A and 17.7 ft of clarity. Below are the top 50 cleanest monitored lakes in Montana, ranked by EPA water quality score.
Ranked List
| # | Lake | County | Grade | Clarity | Phosphorus | Algae |
|---|---|---|---|---|---|---|
| 1 | Big Sky Lake South Hole | Missoula | A | 17.7 ft | 9.6 µg/L | - |
| 2 | Tally Lake | Flathead | A | 15.2 ft | 4.5 µg/L | 0.9 µg/L |
| 3 | Nla Lake | Granite | A | 28.4 ft | 6.4 µg/L | 0.8 µg/L |
| 4 | Nla Lake | Missoula | A | 41.9 ft | 3.7 µg/L | 0.4 µg/L |
| 5 | Nla Lake | Flathead | A | 47.6 ft | 1.1 µg/L | 0.6 µg/L |
| 6 | Nla Lake | Flathead | A | 20 ft | 13.8 µg/L | 1.1 µg/L |
| 7 | Nla Lake | Lewis and Clark | A | 15.9 ft | 12.3 µg/L | 0.8 µg/L |
| 8 | Nla Lake | Lincoln | A | 16.9 ft | 13.8 µg/L | 2.5 µg/L |
| 9 | Nla Lake | Lincoln | A | 25.4 ft | 13.4 µg/L | 1.3 µg/L |
| 10 | Nla Lake | Lake | A | 32.3 ft | 7.8 µg/L | 0.9 µg/L |
| 11 | Nla Lake | Ravalli | A | 18 ft | 6.9 µg/L | 0.9 µg/L |
| 12 | Lake Alva Mid-Lake Deep | Missoula | A | 21.6 ft | 6.6 µg/L | - |
| 13 | Seeley Lake Middle Basin | Missoula | A | 15.4 ft | 8.1 µg/L | - |
| 14 | Whitefish Lake | Flathead | A | 22 ft | 3 µg/L | 1.1 µg/L |
| 15 | Whitefish Lake | Flathead | A | 23.5 ft | 3.3 µg/L | 1.6 µg/L |
| 16 | Placid Lake Midlake Hole | Missoula | A | 16.5 ft | 8 µg/L | - |
| 17 | Lake Inez South Hole | Missoula | A | 17.8 ft | 12.1 µg/L | - |
| 18 | Lake Koocanusa | Lincoln | A | - | 4 µg/L | 2.3 µg/L |
| 19 | Lake Koocanusa | Lincoln | A | - | 4.5 µg/L | 1.4 µg/L |
| 20 | Salmon Lake Mid-North Basin | Missoula | A | 17 ft | 11.3 µg/L | - |
| 21 | Lake Mary Ronan East Location | Lake | A | 15.1 ft | 9 µg/L | 4.3 µg/L |
| 22 | Swan Lake South End | Lake | A | - | 3.7 µg/L | 1.3 µg/L |
| 23 | Hanson-Doyle Lake | Flathead | A | - | 7.3 µg/L | 2.3 µg/L |
| 24 | Loon Lake | Lake | A | - | 6.7 µg/L | 2.2 µg/L |
| 25 | Sophie Lake | Lincoln | A | - | 11.1 µg/L | 2.4 µg/L |
| 26 | Lost Coon Lake | Flathead | A | - | 9.7 µg/L | 2.5 µg/L |
| 27 | Swan Lake North End | Lake | A | - | 3.6 µg/L | 1.2 µg/L |
| 28 | Foys Lake | Flathead | A | - | 15.8 µg/L | 4.1 µg/L |
| 29 | Rogers Lake | Flathead | A | - | 11.6 µg/L | 2.6 µg/L |
| 30 | Beaver Lake | Flathead | A | - | 18.5 µg/L | 3.5 µg/L |
| 31 | Smith Lake | Flathead | A | - | 7.4 µg/L | 1.4 µg/L |
| 32 | Tetrault Lake | Lincoln | A | - | 7.5 µg/L | 3.2 µg/L |
| 33 | Jette Lake | Lake | A | - | 16.6 µg/L | 4.7 µg/L |
| 34 | Mary Ronan Lake East | Lake | A | - | 15.8 µg/L | 4.1 µg/L |
| 35 | Dollar Lake | Flathead | A | - | 7.2 µg/L | 2.9 µg/L |
| 36 | Lake Blaine | Flathead | A | - | 10 µg/L | 2.4 µg/L |
| 37 | Bailey Lake | Flathead | A | - | 7.1 µg/L | 2.2 µg/L |
| 38 | Dickey Lake | Lincoln | A | - | 11.6 µg/L | 2.2 µg/L |
| 39 | Flathead Lake | Flathead | A | - | 2.4 µg/L | 0.6 µg/L |
| 40 | Lake Five | Flathead | A | - | 10.6 µg/L | 3.7 µg/L |
| 41 | Flathead Lake | Lake | A | - | 3.6 µg/L | 0.8 µg/L |
| 42 | Spencer Lake | Flathead | A | - | 8.8 µg/L | 2.6 µg/L |
| 43 | Ashley Lake | Flathead | A | - | 9.8 µg/L | 2.1 µg/L |
| 44 | Fish Lake | Lincoln | A | - | 9.5 µg/L | 2.3 µg/L |
| 45 | Peterson Lake | Flathead | A | - | 7.6 µg/L | 1.5 µg/L |
| 46 | Flathead Lake | Lake | A | - | 2.6 µg/L | 0.6 µg/L |
| 47 | Blanchard Lake | Flathead | A | - | 5.5 µg/L | 1.4 µg/L |
| 48 | Abbot Lake | Flathead | A | - | 9 µg/L | 2 µg/L |
| 49 | Murray Lake | Flathead | A | - | 13.4 µg/L | 4.2 µg/L |
| 50 | Murphy Lake | Lincoln | A | - | 6.5 µg/L | 1.8 µg/L |