Gallatin River Fly Fishing Report - August 16, 2026

Fly Fishing Report

GALLATIN RIVER

Report
AUG 16 — 23, 2026
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Flow
482CFS
Gallatin River near Gallatin Gateway, MT
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Water Temp
Updated 2026-08-16
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Weather
47–81°F
Slight Chance Rain Showers
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Clarity
Clear
Check post-storm
Flow is running 482 cfs at 1.61 ft gauge height near Gallatin Gateway — slightly elevated from last week but still clean and very wadeable. Morning windows are prime before afternoon heat builds toward the 80°F high; a slight chance of afternoon thunderstorms (3–5 PM) could trigger a feeding flurry, so stay alert.
Hatch Chart
Insect Size Activity Prime Time
Spruce Moth 12-14 Moderate 9 AM - 2 PM
Grasshopper / Terrestrials 10-12 Moderate 11 AM - 3 PM
Ants 14-16 Moderate 10 AM - 2 PM
Baetis (BWO) 20-22 Light 3 PM - 6 PM
Caddis 16-18 Light 7 AM - 10 AM
Midge 20-22 Light 7 AM - 9 AM
Best Time Window
  • 7 AM - 10 AM: Prime dry fly window — hoppers, ants, and caddis on canyon pocket water before the sun fully hits.
  • 10 AM - 1 PM: Nymph the deeper slots and boulder seams as surface activity slows; Frenchies and Straggle Stones shine.
  • 3 PM - 6 PM: Watch for afternoon storm clouds to trigger a BWO hatch on tailouts; switch to small dries and emergers.
Guide's Tip
From the benchGet on the water by 7 AM and focus your dry fly game on the canyon pocket water — fish are actively feeding before the sun hits the water and temperatures climb. Slap hoppers and ants tight to the bank structure and undercut rocks, then let the fly dead-drift without any mending for at least 3–4 feet before picking up. If afternoon thunderstorms materialize around 3–5 PM, don't leave — that low-light window often triggers a short but intense BWO hatch on the tailouts; switch to a #22 Parachute BWO and work the flat water below riffles. Keep a close eye on water temperature in the lower valley sections and plan to wrap up fishing there well before midday.
Main Species
Brown Trout
Rainbow Trout
Westslope Cutthroat Trout
Report generated August 16, 2026 — Next update: August 23, 2026