Ignore the name
Read the river before you read the water. Big Sky Fishing says the Stillwater has significant whitewater, large drops, and rocks that are slick, loose and everywhere, and the popular stretches below Nye carry Class II and III rapids that only experienced rowers should run. Wikipedia's entry says the section from Nye to Cliff Swallow is not recommended for floating when the gauge is above 4.5 feet because of several low bridges, that Cliff Swallow to Johnson Bridge is the safer float, and that the heaviest rapids, including the Beartooth Drop, are below Swinging Bridge FAS, where commercial whitewater companies run in summer. Big Sky also flags a diversion dam near the Johnson Creek bridge. Wade in felt or studs with a staff, and scout anything you have not floated.
Buffalo Jump to Cliff Swallow, along Highway 420
The Stillwater rises in the Absaroka-Beartooth Wilderness and runs more than twenty miles inside it, most of it Class V or worse and not floatable, then rapids continue to Nye, eight miles below the wilderness boundary. The fish up there, per Big Sky, are cutthroat, rainbows and brook trout of 8 to 10 inches with the occasional golden, and Lake Sioux Charley is the one slow stretch above Nye. The public water starts at Buffalo Jump FAS, off Highway 419 at Nye, at river mile 35.2. Moraine FAS (mile 32.1) and Castle Rock FAS (mile 30.8) sit 16.1 and 15 miles west of Absarokee on Highway 420, and Cliff Swallow FAS (mile 23.4), 9 miles west of town, has a wheelchair ramp to a fishing platform. All four are hand launches with camping; Castle Rock charges $12 a night with a valid fishing license and $18 without. Big Sky warns that by late summer large rafts scrape between Buffalo Jump and Cliff Swallow, especially around Castle Rock and Moraine. This is pocket water: fish the soft spots behind boulders and the seams along the bank.
Absarokee to the Yellowstone
Rosebud Creek comes in near Absarokee and the river gets bigger. Absaroka FAS (FWP's spelling), a mile west of town by the Johnson Bridge road at river mile 13.7, is the main hand launch here, and Jeffrey's Landing FAS, 1.5 miles north of Absarokee on Highway 78, sits right beside the USGS gauge. Downstream, Whitebird FAS (mile 5.8, gravel ramp) and Swinging Bridge FAS (mile 5) are both off Highway 78 just south of Columbus, and Fireman's Point, with a raft slide, is at mile 1.9 near the confluence. Big Sky says browns below Nye average 12 to 14 inches and can top twenty, with rainbows around 12. Rainbows run up from the Yellowstone to spawn in spring, some as far as Nye, and browns follow in the fall; Montana Angler says the fall run is real but not a major one. The June 2022 flood hit this valley hard, and East Rosebud Fly and Tackle's current fall report says fish numbers are slowly coming back.
No special rules, so the Central District ones apply
Do not be misled by the 2026 FWP regulation book: the only Stillwater River entry in it is the Flathead-drainage Stillwater in the Western District. This Stillwater has no exception listed, so FWP's Central District standards govern it. The season is open all year, at all hours. You may keep 3 trout daily and in possession, only 1 over 18 inches and only 1 cutthroat; brook trout 20; whitefish 20 daily and 40 in possession. Arctic grayling go back immediately. Live fish may not be used as bait, though worms and insects are allowed, and one line with two hooks is the river limit. Lakes in the Absaroka-Beartooth Wilderness above carry a 10 trout limit. The Stillwater was not on FWP's hoot-owl or closure list as of September 24, 2026.
What 330 cfs at Absarokee looks like
The Absarokee gauge averages 3,465 cfs in June and 2,284 in July, then falls to 838 in August, 583 in September and 519 in October. Sweetwater Fly Shop runs its Stillwater raft trips from early July to mid-August, which matches the tail of runoff. East Rosebud Fly and Tackle's fall report calls 330 cfs very low and manageable for wading, with water in the mid 50s, and Montana Angler describes the late-season river as low and bony and best waded. No shop publishes a full range, so the 330 to 840 cfs band on this page runs from East Rosebud's wading flow up to the August mean, the part of the year when the river is both fishable and safe to wade. Flows held between 341 and 608 cfs in the two weeks to September 24, 2026.
Big dries in fast water
Montana Angler's hatch chart says the Stillwater's hatches are sporadic compared with neighboring rivers, and that fits the water: trout here have a second to decide, so they eat attractors. Blue-winged olives come late March through May and again mid-September into October, best below Nye on gray days. Mother's Day caddis show in early May, and caddis hatch again from mid-June through August, with strong evening flights. Salmonflies come as the river drops off runoff, followed by golden stones, size 8 to 12, from late June to mid-July, Yellow Sallies and size 16 PMDs. Spruce moths fall off the timbered banks from mid-July to mid-August. The main event is terrestrials from mid-July to early September; Montana Angler likes tan, grey, pink and yellow hoppers, Big Sky says hoppers work from July through mid-September, and a Royal Wulff is a standing favorite. East Rosebud's fall list is the Pink Pookie, Chubby Chernobyl, perdigons and Prince nymphs. Montana Angler notes the river cools early and is not much of a late fall or winter fishery.