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Is it too cold to swim in Flathead Lake?
The latest NASA JPL satellite analysis, dated November 3, 2026, gives 53°F (11.7°C) at the nearest water pixel. That is very cold water.
Between 50°F and 60°F, rated very dangerous to immediately life-threatening: the range where most unacclimated people have a maximum cold shock response. Temperature is only one factor: check rip current and surf alerts, and swim near lifeguards.
How cold is too cold to swim?Water temperature through the year
Average water temperature by month, satellite 2016–2025. Warmest in July.
Average water temperature by month
| Month | Average | Coldest year | Warmest year |
|---|---|---|---|
| January | 38°F | 35°F | 41°F |
| February | 38°F | 35°F | 41°F |
| March | 42°F | 39°F | 44°F |
| April | 45°F | 42°F | 47°F |
| May | 53°F | 49°F | 55°F |
| June | 62°F | 58°F | 64°F |
| July | 67°F | 63°F | 70°F |
| August | 64°F | 59°F | 69°F |
| September | 59°F | 56°F | 64°F |
| October | 50°F | 47°F | 54°F |
| November | 44°F | 39°F | 49°F |
| December | 40°F | 37°F | 43°F |
Water temperatures nearby
Frequently asked questions
Is it too cold to swim in Flathead Lake?
The latest NASA JPL satellite analysis, dated November 3, 2026, gives 53°F (11.7°C) at the nearest water pixel. That is very cold water. Between 50°F and 60°F, rated very dangerous to immediately life-threatening: the range where most unacclimated people have a maximum cold shock response. Temperature is only one factor: check rip current and surf alerts, and swim near lifeguards. How cold is too cold?
When is the water warmest at Flathead Lake?
Based on satellite data from 2016 to 2025, the water is warmest in July (average 67°F) and coldest in January (average 38°F).
Where does this water temperature come from?
We show NASA JPL’s daily MUR satellite analysis for the nearest water, about 0.0 mi away, when no suitable current in-water sensor is available. Satellite values are typically a degree or two cooler than afternoon readings at the shore. Satellite vs. buoy temperatures.
Sources: NASA JPL MUR satellite analysis; forecast and alerts from the National Weather Service. Readings are provisional. All Montana water temperatures · Methodology