Tuolumne River at Grand Canyon Of Tuolumne above Hetch Hetchy
Tuolumne River · Sierra / West · USGS gage 11274790
Trout (marginal) (summer mean 19.0°C — trout, warm in summer).
Water
71°F
Flow
61 cfs
Air
80°F
Sky
0%
Pressure
29.86 in
Wind
6 mph
Predicted hatches · 2026-07-31
PredictedSlate Drake / IsonychiaIsonychia spp.0.73
Predicted by conditions; no reports yet. water 21.8°C (71°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
PredictedHopper / TerrestrialsAcrididae (grasshoppers)0.56
Predicted by conditions; no reports yet. water 21.8°C (71°F) sits in the prime band (17-24°C); shoulder of the season; 8 days sustained ≥14°C; warm sun favors it; watch warm, breezy afternoons.
flies: Morrish Hopper #8-12, Chubby Chernobyl, Dave's Hopper
PredictedHexagenia (Hex)Hexagenia limbata0.55
Predicted by conditions; no reports yet. water 21.8°C (71°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.0.37
Predicted by conditions; no reports yet. water 21.8°C (71°F) is cooling past 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
PredictedLight CahillStenacron / Stenonema0.20
water 21.8°C (71°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
PREDICTED from the first-principles model only. Report-confirmed signal (fly-shop & forum reports) is the next milestone.