
Prosopium williamsoni
Native mountain whitefish in western trout rivers, a good winter nymphing fish.
Find on map ↓Locations with source-linked species records. Open a river on its state map.

Mountain whitefishSelway Park
Seasonal closure: Closed to fishing Oct 1 to Mar 31 on this stretch; the planner leaves it out then.
View river on mapBrook, brown, rainbow trout documented for this water (survey). Stocking or surveys do not guarantee fish at this entrance. FWP fish distribution layer records Brook Trout, Brown Trout, Rainbow Trout on the Beaverhead River at this site; also westslope cutthroat in the stream-wide list, plus mountain whitefish/burbot nearby.
Source checked 2026-10-25.
This reach (Barretts Diversion to the mouth) is open April 1 through Sept. 30 only; brown trout catch-and-release; rainbow trout catch-and-release on the entire river; single-point hooks. A conservation license is required to use FWP fishing access sites (nonresident $10; included with a fishing license). Check current Montana trout regulations for this water.
Current fishing regulations ↗
Mountain whitefishPowerhouse
Seasonal closure: Closed to fishing Oct 1 to Mar 31 on this stretch; the planner leaves it out then.
View river on mapBrook, brown, rainbow trout documented for this water (survey). Stocking or surveys do not guarantee fish at this entrance. FWP fish distribution layer records Brook Trout, Brown Trout, Rainbow Trout on the Big Hole River at this site; also mountain whitefish, arctic grayling and cutthroat.
Source checked 2026-10-25.
Below Dickie Bridge the Big Hole is open April 1 through Sept. 30 only (annual brown trout spawning closure), catch-and-release with single-point hooks; arctic grayling catch-and-release. A conservation license is required to use FWP fishing access sites (nonresident $10; included with a fishing license). Check current Montana trout regulations for this water.
Current fishing regulations ↗
Mountain whitefishLazy KB
View river on mapBrook, brown, rainbow trout documented for this water (survey). Stocking or surveys do not guarantee fish at this entrance. FWP fish distribution layer records Brook Trout, Brown Trout, Rainbow Trout on the Big Spring Creek at this site; also mountain whitefish.
Source checked 2026-10-25.
Central District standard: streams open all year unless an exception applies. The Central exceptions pages of the 2026 FWP booklet could not be read; the 2023 exceptions list showed no season exception for this water — confirm before fishing. A conservation license is required to use FWP fishing access sites (nonresident $10; included with a fishing license). Check current Montana trout regulations for this water.
Current fishing regulations ↗
Mountain whitefishDarby Bridge
View river on mapBrook, brown, rainbow trout documented for this water (survey). Stocking or surveys do not guarantee fish at this entrance. FWP fish distribution layer records Brook Trout, Brown Trout, Rainbow Trout on the Bitterroot River at this site; also westslope cutthroat, bull trout and mountain whitefish.
Source checked 2026-10-25.
Bitterroot River is open all year: general season third Saturday in May - Nov. 30; Dec. 1 to third Saturday in May is catch-and-release for all trout; artificial lures, maggots or aquatic insects only. A conservation license is required to use FWP fishing access sites (nonresident $10; included with a fishing license). Check current Montana trout regulations for this water.
Current fishing regulations ↗
Mountain whitefishK. Ross Toole
View river on mapBrook, brown, rainbow trout documented for this water (survey). Stocking or surveys do not guarantee fish at this entrance. FWP fish distribution layer records Brook Trout, Brown Trout, Rainbow Trout on the Blackfoot River at this site; also westslope cutthroat, bull trout and mountain whitefish.
Source checked 2026-10-25.
Walk-in access only, no facilities. Mainstem open all year: general season third Saturday in May - Nov. 30 (cutthroat catch-and-release, 3 combined trout); Dec. 1 to third Saturday in May artificial lures and/or maggots only. A conservation license is required to use FWP fishing access sites (nonresident $10; included with a fishing license). Check current Montana trout regulations for this water.
Current fishing regulations ↗
Mountain whitefishBig Rock
View river on mapBrown, rainbow trout documented for this water (survey). Stocking or surveys do not guarantee fish at this entrance. FWP fish distribution layer records Brown Trout, Rainbow Trout on the Boulder River at this site; also mountain whitefish; brook trout and Yellowstone cutthroat appear elsewhere on the stream but not on this reach.
Source checked 2026-10-25.
Trailer limit 20 ft, 7-day stay. Central District standard: streams open all year unless an exception applies. The Central exceptions pages of the 2026 FWP booklet could not be read; the 2023 exceptions list showed no season exception for this water — confirm before fishing. A conservation license is required to use FWP fishing access sites (nonresident $10; included with a fishing license). Check current Montana trout regulations for this water.
Current fishing regulations ↗Hover or focus a landscape to see the fish. Choose Fish illustration on touch screens.
Map links open the recorded river. A record documents species presence, not current abundance or permission to target a fish. These maps may not have an individual filter for this species.
Local-water cards link to the evidence supporting the species record and the river on its state map. Records do not establish current abundance or catch rates. Historic records are labeled separately. Check the fishing rules before targeting a species.
Identification references for this illustration: