Big Hole River Near Melrose
Big Hole River · Rockies · USGS gage 06025500
Trout (marginal) (summer mean 17.8°C — trout, warm in summer).
Water
70°F
Flow
496 cfs
Air
68°F
Sky
0%
Pressure
29.87 in
Wind
6 mph
Predicted hatches · 2026-07-31
PredictedSlate Drake / IsonychiaIsonychia spp.1.00
Predicted by conditions; no reports yet. water 21.0°C (70°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
PredictedHexagenia (Hex)Hexagenia limbata0.55
Predicted by conditions; no reports yet. water 21.0°C (70°F) sits in the prime band (19-23°C); shoulder of the season; 8 days sustained ≥18°C; bright moon — night activity; watch after dark — the famous night hatch.
flies: Hex Dun #4-8, Hex Nymph, Hex Spinner
PredictedTricoTricorythodes spp.0.50
Predicted by conditions; no reports yet. water 21.0°C (70°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)0.50
Predicted by conditions; no reports yet. water 21.0°C (70°F) sits in the prime band (17-24°C); shoulder of the season; 8 days sustained ≥14°C; watch warm, breezy afternoons.
flies: Morrish Hopper #8-12, Chubby Chernobyl, Dave's Hopper
PredictedSpotted / Summer CaddisHydropsyche spp.0.33
water 21.0°C (70°F) is cooling past the prime band (14-19°C); peak season; 8 days sustained ≥12°C; watch evening, last hour of light.
flies: Elk Hair Caddis #14-16, Iris Caddis, X-Caddis
PredictedLight CahillStenacron / Stenonema0.33
water 21.0°C (70°F) is cooling past the prime band (16-20°C); shoulder of the season; 8 days sustained ≥15°C; watch dusk.
flies: Light Cahill #14-16, Cream Cahill, Cahill Spinner
PredictedSulphurEphemerella dorothea / invaria0.17
water 21.0°C (70°F) is cooling past the prime band (15-19°C); shoulder of the season; 8 days sustained ≥13°C; watch evening, the last two hours of light.
flies: Sulphur Comparadun #16-18, Sulphur Spinner, Pheasant Tail
PREDICTED from the first-principles model only. Report-confirmed signal (fly-shop & forum reports) is the next milestone.