Flathead Lake fishing: Largemouth Bass, Rainbow Trout, Northern Pike
Target species: Largemouth Bass, Rainbow Trout, Northern Pike, Smallmouth Bass, Cutthroat Trout, Brook Trout, Lake Trout
Best months: Jul, Aug, Sep for Largemouth Bass
Second window: May, Jun, Sep, Oct for Rainbow Trout
Boat: 4 ramps and launches on file for this water.
Start here: Launch at Bigfork.
The lake
Flathead Lake covers 123,314 acres in Montana, across 2 counties: Lake and Flathead. It is a lake: 90.5% of it is 280 feet deep or less; the deepest point measured is at least 380 feet (115.8 m). Our records hold 12 species for this water.
Depth and bottom
Deepest measured point: at least 380 ft (115.8 m). That is the deepest contour line: the bottom goes deeper. 90.5% of the water is 280 feet or shallower. We hold 232 depth contour lines for this water.
- 0–20 ft: 16% of the water
- 20–40 ft: 6.5% of the water
- 40–60 ft: 3% of the water
- 60–80 ft: 5.9% of the water
- 80–100 ft: 7.2% of the water
- 100–120 ft: 6% of the water
- 120–140 ft: 5.8% of the water
- 140–160 ft: 6.6% of the water
- 160–180 ft: 5.8% of the water
- 180–200 ft: 5.5% of the water
- 200–220 ft: 4.4% of the water
- 220–240 ft: 3.3% of the water
- 240–260 ft: 6.5% of the water
- 260–280 ft: 8% of the water
- 280–300 ft: 3.4% of the water
- 300–320 ft: 3.8% of the water
- 320–340 ft: 1.4% of the water
- 340–360 ft: 0.7% of the water
7 target fish, led by Largemouth Bass
- Largemouth Bass — Best months: Jul, Aug, Sep.
- Rainbow Trout — Best months: May, Jun, Sep, Oct.
- Northern Pike — Best months: Jun, Jul, Aug, Sep.
- Smallmouth Bass — Best months: Jun, Jul, Aug, Sep.
- Cutthroat Trout — Best months: May, Jun, Sep, Oct.
- Brook Trout — Best months: May, Jun, Sep, Oct.
- Lake Trout — Best months: May, Jun, Sep, Oct.
Also recorded here: Lake Whitefish, Arctic Grayling, Yellow Perch, Bull Trout, Mountain Whitefish.
Water and conditions
Our water temperature readings average 66°F; they do not cover the whole year, so this is not a yearly average. The coldest single reading we hold is 39°F and the warmest is 77°F; the warmest monthly average is 70°F. pH averages 8.4. These readings span 2017–2026.
Stocking: 107,477,534 fish, 1967–1997
Montana Fish, Wildlife & Parks records list 107,477,534 fish released into this water from 1967 to 1997. The latest stocking on record is from 1997, more than three years ago.
- Cutthroat Trout: 11,811,614 in 1944–1966
- Lake Whitefish: 10,664,630 in 1927–1942
- Rainbow Trout: 7,689,198 in 1928–1950
- Largemouth Bass: 230,184 in 1933–1991
- Brook Trout: 99,165 in 1934–1952
- Arctic Grayling: 90,000 in 1934–1935
- Bull Trout: 20,826 in 1950–1952
- Mountain Whitefish: 20,000 in 1990
5 more species on the stocking list.
4 ramps and launches on this water
On this water we hold 4 boat ramps.
- Bigfork website myfwp.mt.gov/fishMT/fas/39753993
- Flathead Lake Private Harbor phone +14068330940 · website flatheadlakeprivateharbor.com
- Somers website myfwp.mt.gov/fishMT/fas/39754047
- Walstad website myfwp.mt.gov/fishMT/fas/39754043
Fee and opening hours are blank for all 4 places in this list: a blank means we hold no such field, not that it is free or always open, and this list may not be complete.
What is hard here
Wind is the limit, not the fish: 123,314 acres of open water build a short steep chop, and there is no shelter in the middle.
Where this data comes from
- Montana Fish, Wildlife & Parks — Montana Fish, Wildlife & Parks: depth contours: class A, a survey of the bottom.
- Webster, K.E., McCullough, I.M., Soranno, P.A. LAGOS-US DEPTH v1.0, EDI, doi:10.6073/pasta/64ddc4d04661d9aef4bd702dc5d8984f (CC BY 4.0); Cheruvelil et al. LAGOS-US LOCUS v1.0 (EDI) — LAGOS-US DEPTH v1.0: Lake depth for 17,675 lakes in the conterminous U.S.: class B, a depth figure measured and published by an agency, without a bottom map.
