Reservoir · United States
Flathead Lake
Large natural lake in Lake and Flathead counties in Montana, United States
- Area
- 487km²
- Max depth
- 113m
- Average depth
- 4.5m
- Elevation
- 880m a.s.l.
- Shoreline
- 249km
- Volume
- 2.2km³
Flathead Lake is a reservoir in United States. It covers 487 km². On average it is 4.5 m deep, and 113 m at its deepest point. Its surface lies 880 m above sea level.
Plan your visit
Stay, sail and get there
Some links above are affiliate links: if you book through them we may earn a commission, at no extra cost to you. It never changes what the data on this page says.
The water
How warm is Flathead Lake?
The water is warmest in July, around 20 °C at the surface, and coldest in February, around 0 °C. It rarely averages 20 °C, but it stays above 17 °C from July to August: brisk, refreshing swimming.
It does not normally freeze in winter.
On the shore, afternoons reach 26 °C on average in July and -4 °C in December. The driest month is July (25 mm of rain), the wettest June (85 mm).
Average surface temperature measured by the Landsat 8 satellite between 2013 and 2021 at the point furthest from the shore (70 readings). Shallow bays and beaches are often warmer.
From above
The whole lake from space
Month by month
The year at the lake, month by month
Not a forecast: these are averages over many years. Water is the 2013–2021 average; air, rain, sun and wind are the 1991–2020 average.
Water: 2013–2021 averageClimate: 1991–2020 average
| Month | Water°C | Water high°C | Air high°C | Air low°C | Rainmm | Rainy daysdays | Sunh/day | Windkm/h |
|---|---|---|---|---|---|---|---|---|
| January | 1 | 2 | -3 | -11 | 76 | 17 | 2.3 | 7 |
| February | 0 | 1 | -2 | -11 | 62 | 14 | 4.2 | 7 |
| March | 2 | 4 | 3 | -6 | 72 | 16 | 5.1 | 8 |
| April | 6 | 8 | 9 | -2 | 65 | 15 | 6.5 | 8 |
| May | 11 | 14 | 15 | 4 | 72 | 15 | 7.9 | 8 |
| June | 16 | 18 | 19 | 8 | 85 | 15 | 8.4 | 7 |
| July | 20 | 20 | 26 | 12 | 25 | 7 | 12.0 | 7 |
| August | 20 | 20 | 26 | 11 | 29 | 7 | 10.0 | 7 |
| September | 17 | 18 | 20 | 6 | 41 | 8 | 7.4 | 7 |
| October | 12 | 14 | 10 | 0 | 63 | 12 | 4.6 | 7 |
| November | 7 | 9 | 2 | -6 | 74 | 16 | 2.1 | 7 |
| December | 3 | 5 | -4 | -11 | 76 | 16 | 1.5 | 7 |
Water: LakeTEMP (Landsat 8, 2013–2021). Air, rain, sun and wind: NASA POWER, 1991–2020 averages. A rainy day has at least 1 mm of rain. Sunshine hours are derived from measured solar radiation.
Size & depth
How big, how deep
- On average, water stays in the lake for about 3 months before flowing out.
- Its catchment drains 18,296 km² of land.
- About 316 m³ of water flow out every second, on average.
- Its shoreline is 3.2 times longer than a circle of the same area: plenty of bays and inlets.
Around the shore
What's around Flathead Lake
Counted within 1.5 km of the shoreline in OpenStreetMap, the map anyone can edit.
- 7beaches and swimming spots
Long Beach, Riverside Park Swimming Access, Sacajawea Swimming Access, Salish Point Swimming Access, Boettcher Park Swimming Access and 2 more
- 10campsites
Wayfarers State Park Campground, Flathead River RV Resort, Polson / Flathead Lake KOA Holiday, Big Arm Unit, Polson Motorcoach Resort and 5 more
- 1boat hire and water-sport clubs
Woods Bay Marine Services
- 18marinas and slipways
North Flathead Yacht Club, Eagle Bend Yacht Harbour, Flathead Lake Private Harbor and 15 more
- —ferry piers
- 2viewpoints
- 33hotels, B&Bs and chalets
Flathead Lake Resort, KwaTaqNuk Resort, Port Polson Inn, Edgewater RV Resort & Motel, Bayview Inn and 28 more
- —fishing spots
- 23restaurants and cafés
Towns on the shore
- Polson4,707 people
- Bigfork4,270 people
- Lakeside2,669 people
- Somers1,109 people
Nearest airport with scheduled flights: Glacier Park International Airport (FCA), 43 km in a straight line.
Car hire at FCA airport (Kalispell)Discover Cars · Affiliate linkOpenStreetMap is built by volunteers: when a number is low, it may just mean nobody has mapped it yet.
Recent years
How each month compared
Afternoon high on the shore. The first row is the reference, the 1991–2020 average in °C; the years below show the difference from it: warmer in orange, cooler in blue.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1991–2020 average | -3.4 | -2.3 | 2.8 | 8.8 | 15.3 | 19.4 | 26.2 | 26.0 | 19.7 | 10.1 | 1.8 | -3.5 |
| 2020 | +2.2 | +2.4 | +0.5 | −0.2 | −0.2 | −0.8 | −1.4 | +0.7 | +1.5 | −1.0 | −0.1 | +2.8 |
| 2021 | +2.7 | −2.6 | +2.9 | +1.3 | −0.2 | +4.8 | +5.0 | −0.8 | +0.5 | +2.1 | +2.2 | −0.3 |
| 2022 | +0.1 | −0.1 | +1.9 | −3.1 | −2.4 | −0.6 | +1.4 | +3.1 | +3.2 | +5.0 | −3.6 | −1.9 |
| 2023 | +0.8 | +0.6 | −1.3 | +0.6 | +4.2 | +2.3 | +2.7 | +1.0 | −0.2 | +1.8 | +0.7 | +4.1 |
| 2024 | −0.5 | +3.3 | +2.6 | +1.5 | −1.0 | +0.4 | +2.8 | ±0.0 | +2.4 | +3.4 | +0.1 | +3.2 |
| 2025 | −1.4 | −2.9 | +3.0 | +1.9 | +2.4 | +2.8 | +0.3 | +0.5 | +5.0 | +0.4 | +3.2 | +4.4 |
+1 warmer than usual −1 cooler than usual
Nearby
More lakes nearby
United States27.1 km² · 75 km away19°maxSaint Mary LakeUnited States15.0 km² · 96 km away16°maxLake Pend OreilleUnited States360 km² · 168 km away21°maxCoeur D'Alene LakeUnited States126 km² · 206 km away22°maxKootenay Lake
Canada422 km² · 253 km away19°maxBerkeley PitUnited States1.1 km² · 245 km away25°maxAbout these numbers
| Outline, area, depth, volume | HydroLAKES v1.0 (Messager et al. 2016) · CC BY 4.0 |
|---|---|
| Water temperature and ice | LakeTEMP v1 (Korver et al. 2024), Landsat 8 2013–2021 · CC BY 4.0 |
| Air, rain, sun, wind | NASA POWER, 1991–2020 · public domain |
| Names and description | Wikidata (Q1427364) · CC0 |
| Around the shore | © OpenStreetMap contributors · ODbL |
| Images | EOX Sentinel-2 cloudless 2016 · CC BY 4.0; Wikimedia Commons |
Every figure is an average or a count from a public dataset. Licences and methods: data sources.
