Planning a Fall Trip to the Henry's Fork
Low water, tiny mayflies and quiet banks. How I'm planning a late-fall Henry's Fork trip, section by section, and what I'm checking before I drive.
There are rivers I fish, and there are rivers I go back to. The Henry's Fork is one of the second kind.
I'm heading back this fall, and it won't be the same river I left. 2026 has been a very dry year up there. The Henry's Fork Foundation says Island Park Reservoir was drained to about 12% full in September to send water to farms downstream, and for a while that pushed murky water into Box Canyon. Mid-October reports from guides describe a river running very low and weedy, but cold, clear and full of feeding fish.
Where I'm going
I'll start in Box Canyon, wading instead of floating. At these flows a boat just scrapes over the boulders. I'll work the deeper pockets with small nymphs (flies that sink and imitate young insects) and lean hard on a wading staff.
Then the Railroad Ranch in Harriman State Park, the stretch I think about most. Wide, flat, clear water where rainbows sip bugs you can barely see. In fall it's a place to walk slowly, find one rising fish, and try not to spook it.
If there's time, I'll drop down below Ashton. Fall is brown trout spawning season there, so I'll watch for redds, the pale, clean patches of gravel where they lay eggs, and stay off them.
What I'm bringing
The fall bugs are small: blue-winged olives, tiny pseudo mayflies, and mahogany duns. They hatch best on gray, mild days around midday. Mornings mean nymphs or streamers (bigger flies that look like small fish), then small dry flies once the bugs come off.
Before I drive
I'll check the Henry's Fork gauges on the map for flow compared with normal (expect "below average" this year), plus water temperature and wind. Wind on the Ranch turns tiny dry flies into a lost cause. I'll save the area offline for the stretches with no signal.
I'll report back on what I find.
-Matt