Missoula County Lake Quality

There are 46 monitored lakes in Missoula County. The mix is varied enough that the county-level average tells you the broad strokes, not the choose-this-cabin specifics. 10 of those lakes carry an A–F grade. The county-level summary describes that subset, not every water body listed. The county-wide average lands at B — solid water quality with most lakes carrying clear summer transparency and low-to-moderate phosphorus.

The county's lakes lean shallow, which makes the grades sensitive to wind, sediment-resuspension, and any nutrient inputs from the watershed. The cleanest lake on the books is Inez Lake (A); the most-stressed is Big Sky Lake (C).