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Westslope Cutthroat Trout

Westslope Cutthroat Trout

The Westslope Cutthroat Trout is Montana's state fish, native to waters on both sides of the Continental Divide.

Scientific Name: Oncorhynchus lewisi

Physical Characteristics:
  • Distinguished by distinctive red slashes under the lower jaw, small dark spots concentrated near the tail with none by the pectoral fins, and silvery-greenish coloration.
  • Montana fish typically range 6-16 inches, rarely exceeding 18 inches.

What to know

Habitat Distribution

  • Native to waters on both sides of the Continental Divide.
  • Pure Westslope cutthroat now occupy only 19-27% of their historic Montana range due to habitat loss and hybridization with rainbow and Yellowstone cutthroat trout.
  • The South Fork Flathead River system contains the world's largest genetically pure population.

Key Locations

  • Upper Flathead River system (including South Fork), Blackfoot River, Rock Creek, upper Missouri River tributaries, and headwater streams in the Bob Marshall Wilderness.
  • Found in the Kootenai watershed, Clark Fork watershed, upper Missouri River drainage including the Judith, Milk, and Marias Rivers, and Saskatchewan River headwaters.

Specific Spots

  • Target areas with pool habitat, overhead cover, and gravel substrates.
  • Focus on riffle-pool complexes, and areas with large substrate providing cover.
  • Fish tend to be in 2nd and 3rd order streams during peak seasons.
  • Small dark flies clustered near pools and riffles.

Westslope Cutthroat Trout FAQ

Answers from onWater's species guide.

What flies work for Westslope Cutthroat Trout in Montana?

Dr.y flies imitating mayflies (especially Baetis/Blue-Winged Olives), caddisflies, and stoneflies. Effective patterns include small dark flies clustered near pools and riffles. Nymphs and streamers for subsurface fishing.

When is the best time to fish for Westslope Cutthroat Trout in Montana?

Peak fishing during summer months when insect hatches are abundant. Spring offers excellent fishing with less pressure, while summer provides consistent dry fly opportunities. Avoid fishing during spawning periods (March-July when water hits 50°F).

How do you catch Westslope Cutthroat Trout in Montana?

Fly fishing is the preferred method. During spring and summer, match emerging aquatic insects with dry flies. For subsurface fishing, use nymphs and streamers, particularly in deeper pools where adults congregate. A dry-dropper setup with a dry fly on top and nymph below works well.

What do Westslope Cutthroat Trout eat?

Primarily feed on aquatic insects, zooplankton, caddisflies, mayflies, stoneflies, midges, terrestrial insects like ants and beetles, and larger fish may eat sculpin.

Where do Westslope Cutthroat Trout live in Montana?

Native to waters on both sides of the Continental Divide. Pure Westslope cutthroat now occupy only 19-27% of their historic Montana range due to habitat loss and hybridization with rainbow and Yellowstone cutthroat trout. The South Fork Flathead River system contains the world's largest genetically pure population.

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