Yellowstone River Fly Fishing Report - September 20, 2026

Fly Fishing Report

YELLOWSTONE RIVER

Report
SEP 20 — 27, 2026
🌊
Flow
CFS
🌡️
Water Temp
☀️
Weather
40–73°F
Patchy Fog
💧
Clarity
Clear
Check post-storm
Live USGS gauge data is unavailable, but recent web intel puts flow near 1,460–1,710 CFS at gin-clear clarity with water temps in the 55–62°F range — textbook fall conditions. Expect patchy morning fog burning off to partly sunny skies with a high of 65°F and calm winds, setting up a productive all-day window.
Hatch Chart
Insect Size Activity Prime Time
Blue-Winged Olive (Baetis) 20-22 Moderate 11 AM - 2 PM
Grasshopper 10-14 Moderate 12 PM - 4 PM
Terrestrial Ants & Beetles 14-18 Light 10 AM - 3 PM
Caddis 16-20 Light 5 PM - 7 PM
Sculpin / Baitfish (Streamer) 4-8 Moderate 7 AM - 10 AM
Best Time Window
  • 6:30 AM - 9:30 AM: Fog-shrouded streamer hour — swing sculpin and minnow patterns through deep pools and undercut banks before the sun penetrates.
  • 11 AM - 2 PM: BWO hatch window — watch tailouts for rising fish and match with small dries or emergers in the surface film.
  • 12 PM - 4 PM: Prime hopper time — work grassy cutbanks and willow-lined edges with a tan or purple hopper as temperatures peak near 65°F.
Guide's Tip
From the benchWith patchy fog this morning, start with streamers — swing a Sculpzilla or Sparkle Minnow through the deep pools and undercut banks before the sun hits the water. Once the fog lifts around 10 AM and temps climb toward 65°F, switch to a hopper fished tight to grassy cutbanks in Paradise Valley; the calm WNW wind keeps presentations clean. If you see noses during the midday BWO window, downsize to a Parachute BWO or Juju Baetis and target the slow tailouts where fish are sipping emergers just under the film. Keep your indicator depth set at 1.5 to 2 times the water column when nymphing — in this gin-clear water, fish are holding right on the bottom and will reject anything that doesn't track naturally.
Main Species
Yellowstone Cutthroat Trout
Brown Trout
Rainbow Trout
Report generated September 20, 2026 — Next update: September 27, 2026