Jefferson River Near Twin Bridges
Jefferson River · Rockies · USGS gage 06026500
Trout (marginal) (summer mean 19.6°C — trout, warm in summer).
Water
74°F
Flow
547 cfs
Air
78°F
Sky
96%
Pressure
29.84 in
Wind
19 mph
Predicted hatches · 2026-07-31
PredictedHopper / TerrestrialsAcrididae (grasshoppers)0.60
Predicted by conditions; no reports yet. water 23.5°C (74°F) sits in 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
PredictedHexagenia (Hex)Hexagenia limbata0.46
Predicted by conditions; no reports yet. water 23.5°C (74°F) is cooling past 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
PredictedSlate Drake / IsonychiaIsonychia spp.0.17
water 23.5°C (74°F) is cooling past 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
PREDICTED from the first-principles model only. Report-confirmed signal (fly-shop & forum reports) is the next milestone.