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Hatch predictions for 300+ US rivers — built from live water & weather, then confirmed against real fly-shop reports.

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Nf Blackfoot River above Dry Gulch near Ovando

Nf Blackfoot River · Rockies · USGS gage 12338300

Coldwater (summer mean 12.1°C — prime coldwater).

Water
59°F
Flow
306 cfs
Air
81°F
Sky
0%
Pressure
29.82 in
Wind
7 mph
Predicted hatches · 2026-07-31
PredictedPale Morning DunEphemerella spp.1.00
Predicted by conditions; no reports yet. water 14.8°C (59°F) sits in the prime band (13-18°C); peak season; 8 days sustained ≥12°C; watch late morning to early afternoon.
flies: PMD Comparadun #16-18, Sparkle Dun, Pheasant Tail #16
PredictedSpotted / Summer CaddisHydropsyche spp.1.00
Predicted by conditions; no reports yet. water 14.8°C (59°F) sits in 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
PredictedGolden StoneHesperoperla / Calineuria0.60
Predicted by conditions; no reports yet. water 14.8°C (59°F) sits in the prime band (14-18°C); peak season; watch afternoon and evening.
flies: Chubby Chernobyl #8-10, Yellow Stimulator, Pat's Rubber Legs
PredictedSalmonflyPteronarcys californica0.50
Predicted by conditions; no reports yet. water 14.8°C (59°F) sits in the prime band (13-16°C); shoulder of the season; 8 days sustained ≥12°C; watch late morning through evening.
flies: Rogue Foam Salmonfly #4-6, Chubby Chernobyl, Pat's Rubber Legs
PredictedGreen DrakeDrunella spp.0.50
Predicted by conditions; no reports yet. water 14.8°C (59°F) sits in the prime band (11-15°C); shoulder of the season; 8 days sustained ≥10°C; watch midday, often cloudy.
flies: Green Drake Parachute #10-12, Cripple, Hares Ear #10
PredictedSulphurEphemerella dorothea / invaria0.27
water 14.8°C (59°F) is warming toward the prime band (15-19°C); shoulder of the season; watch evening, the last two hours of light.
flies: Sulphur Comparadun #16-18, Sulphur Spinner, Pheasant Tail
PredictedSlate Drake / IsonychiaIsonychia spp.0.24
water 14.8°C (59°F) is warming toward the prime band (16-21°C); peak season; 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.