The main-stem Flathead is the big river everything upstream drains into. The North and Middle Forks meet at Blankenship Bridge, the South Fork ties in just above Columbia Falls, and from there the river runs wide, deep, and glacially clear through the Flathead Valley into Flathead Lake — then continues below the lake out of SKQ (Kerr) Dam near Polson. It's one of the last strongholds of pure-strain wild westslope cutthroat, and it's core bull trout water too (ESA-listed, do-not-target, mandatory release). What sets it apart from the classic southwest Montana rivers is that it fishes as a native-cutthroat dry-fly float, not a rainbow/brown tailwater — you search gin-clear water with attractor dries for eager cutthroat rather than matching a technical hatch.
Practically, it's a drift-boat river. The upper main stem from Blankenship down to Old Steel Bridge is the trout heart of it — wide, frequently deep, steady current with a few small rapids below Blankenship; wading is tough except in late-summer low water. Prime time is July through September once runoff clears, and it fishes dry or dry-dropper almost all summer: Chubby Chernobyls, Amy's Ants, and elk hair caddis up top with a pheasant tail or small nymph off the back. Early season it can push 15,000-20,000 CFS on snowmelt out of Glacier country and blows out; it drops into shape by early-to-mid July most years. The Columbia Falls gauge (USGS 12363000) is the number everyone watches — roughly 4,000-8,000 CFS fishes well for the float, dropping toward 3,000-5,000 by late summer.
The context below Kalispell is different water. The river slows into sloughs and warms, turning into northern pike country more than a trout float as it approaches Flathead Lake. Below the lake, the lower Flathead runs out of SKQ (Kerr) Dam through the Flathead Indian Reservation — completely flow-regulated for power, trophy pike water with some rainbows in the first few miles below the dam, and it requires a CSKT tribal permit (about $10 for three days or $17 a year), not a Montana license. Note the 2024-25 regulation change: the single-hook restriction (no treble or double hooks) now extends down the main stem all the way to Flathead Lake.
| Species | Abundance | Best Season | Size | Notes |
|---|---|---|---|---|
| Westslope Cutthroat Trout | Primary | Jul-Sep | 8-16" | The defining fish — pure-strain wild native population, largely catch-and-release. Eager on attractor dries and dry-droppers once runoff clears. |
| Bull Trout | Present | Closed | Large | Native char, ESA-listed. Do-not-target on the main stem; mandatory immediate release if hooked incidentally. |
| Mountain Whitefish | Abundant | Year-round | 10-16" | Native and prolific. Old Steel Bridge is a known bank whitefish spot for anglers without a boat. |
| Northern Pike | Common | Spring/Fall | To 40"+ | Dominates the slow water and sloughs below Kalispell and below Kerr Dam — genuine trophy pike water and a real fly target on streamers. |
| Rainbow Trout | Common | Jun-Sep | 10-16" | Best rainbow water is the first few miles below SKQ (Kerr) Dam on the lower river. |
| Brown Trout | Present | Fall | 12-20" | Occasional, mixed in below the lake and below the dam on the lower river. |
Native westslope cutthroat and bull trout conservation water. Bull trout are do-not-target with mandatory release on the main stem, single-pointed hooks are required down the main stem to Flathead Lake, and the lower river below Kerr Dam is tribal water requiring a CSKT permit rather than a Montana license.
Columbia Falls, MT