Can you keep a lake trout in Montana?

No minimum size, twenty a day, forty in possession.

FWP source page

Five times the Western District's already-generous standard bag — Flathead Lake is managed for aggressive lake trout removal to protect native bull trout and cutthroat, with a release slot protecting the 30-to-36-inch size class. A tribal permit is required on the lake's southern portion within the Flathead Indian Reservation.

FWP source page

No minimum size, but far fewer than the Western District — three a day.

FWP source page

What we left out on purpose

• Bighorn Lake (a separate water from the Bighorn River this site tracks) carries its own sauger/walleye numbers (6 combined daily, only 3 may be sauger) — not modelled here since this site follows the river, not the lake.
• Gallatin River carries a boat-fishing closure between the Yellowstone National Park boundary and the East Gallatin River, and a fixed general season (third Saturday in May – November 30) on the stretch from Porcupine Creek Road to the West Fork — gear/access rules rather than size or bag numbers, not modelled in this schema.
• The Madison River's Lyons-Bridge-to-Ennis-Bridge stretch is actually two adjoining catch-and-release segments (Lyons–Varney and Varney–Ennis) with a near-identical but not byte-for-byte identical rule (one restricts all trout, the other only rainbow). This site's tracked coordinate sits almost exactly at Varney Bridge, the boundary between them — both are described together rather than forcing a guess about which side of the bridge the coordinate falls on.
• Channel catfish, shovelnose sturgeon, tiger muskie and walleye/sauger are not modelled for these six waters because none of the six carries its own number for them and none is a species this site's water reports actually target.
• Montana's hundreds of further named-water exceptions beyond the six waters this site tracks are not modelled — the same restraint used for Colorado's, Kansas's, Michigan's and Minnesota's named-water exceptions.