Madison River below Hebgen Lake
Madison River · Montana · USGS gage 06038500
Upper Madison just below Hebgen Dam — the 'between the lakes' water near West Yellowstone. Cold, prime coldwater.
Water
61°F
Flow
760 cfs
Air
56°F
Sky
11%
Pressure
29.98 in
Wind
11 mph
Predicted hatches · 2026-09-14
PredictedSlate Drake / IsonychiaIsonychia spp.1.00
Predicted by conditions; no reports yet. water 16.0°C (61°F) sits in the prime band (16-21°C); peak season; 8 days sustained ≥14°C; watch afternoon/evening; nymphs crawl to shore to emerge.
flies: Isonychia #10-12, Slate Drake, Leadwing Coachman
PredictedSpotted / Summer CaddisHydropsyche spp.0.50
Predicted by conditions; no reports yet. water 16.0°C (61°F) sits in the prime band (14-19°C); shoulder of the season; 8 days sustained ≥12°C; watch evening, last hour of light.
flies: Elk Hair Caddis #14-16, Iris Caddis, X-Caddis
PredictedTricoTricorythodes spp.0.50
Predicted by conditions; no reports yet. water 16.0°C (61°F) sits in the prime band (16-21°C); shoulder of the season; 8 days sustained ≥15°C; watch early morning spinner falls.
flies: Trico Spinner #20-24, CDC Trico, Griffith's Gnat
PredictedHopper / TerrestrialsAcrididae (grasshoppers)0.37
Predicted by conditions; no reports yet. water 16.0°C (61°F) is warming toward the prime band (17-24°C); shoulder of the season; 8 days sustained ≥14°C; wind puts terrestrials in play; watch warm, breezy afternoons.
flies: Morrish Hopper #8-12, Chubby Chernobyl, Dave's Hopper
PREDICTED from the first-principles model only. Report-confirmed signal (fly-shop & forum reports) is the next milestone.