Flathead Lake water temp
The swimming season in Flathead Lake lasts only one month - August. During this month, Flathead Lake water temperature does not drop below 68°F and therefore suitable for comfortable swimming. The average water temperature in Flathead Lake in winter reaches 36.3°F, in spring 41.2°F, in summer the average temperature rises to 65.1°F, and in autumn it is 52.7°F.
Flathead Lake water temperature now
You may also be interested in other sections of our site for Flathead Lake: Sunrise and Sunset
Flathead Lake water temperature by month
These figures shows the average, minimum and maximum monthly water temperature in Flathead Lake. In addition to the table values, the graph below displays of changes average surface temperature during the year. Values are calculated based on the data over the past 10 years.
| Month | Avr | Min | Max | |
|---|---|---|---|---|
| January | 35.6°F | 33.6°F | 37°F | cold |
| February | 34.7°F | 32.2°F | 37.8°F | cold |
| March | 34.7°F | 32.2°F | 38.5°F | cold |
| April | 39.7°F | 35.1°F | 45.5°F | cold |
| May | 49.5°F | 40.5°F | 56.8°F | cold |
| June | 59.5°F | 53.2°F | 66.7°F | cold |
| July | 67.3°F | 61.3°F | 73.9°F | cold |
| August | 68.7°F | 64.4°F | 72°F | warm |
| September | 61.7°F | 57.2°F | 69.3°F | cold |
| October | 51.6°F | 46.8°F | 59°F | cold |
| November | 44.8°F | 41.5°F | 50°F | cold |
| December | 38.7°F | 35.4°F | 42.6°F | cold |
Chart monthly average water temperature in Flathead Lake
Current temperature and weather
Data in a table show Flathead Lake temperature today (October 1, 2025). For more information and forecast for a few days, go to the weather forecast Flathead Lake.
| 0-3 h | 3-6 h | 6-9 h | 9-12 h |
|---|---|---|---|
 | | |  |
| 53.4°F | 52.7°F | 52.3°F | 54.3°F |
| 12-15 h | 15-18 h | 18-21 h | 21-24 h |
|---|---|---|---|
| | |  |
| 61.3°F | 65.3°F | 60.3°F | 54.9°F |
