Yellowstone River · hatch chart
Closed to protect spawning until the third Saturday in July on much of the Montana reach; late July to October is the season
By month
JanFebMarAprMayJunJulAugSepOctNovDec
| Month | Insect | Stage | Size | Time | Intensity |
|---|---|---|---|---|---|
| Jul | Salmonfly (Pteronarcys californica) | Adult | #4-8 | 10:00-16:00 | |
| Jul | Golden Stone (Perlidae) | Adult | #8-10 | All day | |
| Aug | Spruce Moth | Adult | #12-14 | 14:00-19:00 | |
| Aug | Yellow Sally (Isoperla) | Adult | #14-16 | 11:00-17:00 | |
| Sep | Hoppers and ants | Adult | #8-14 | 10:00-17:00 | |
| Sep | Heptagenia mayflies | Dun | #14-16 | 13:00-17:00 | |
| Oct | Blue-Winged Olive (Baetis) | Dun | #18 | 13:00-16:00 |
Flow and visibility
This is a snowmelt river and the hydrograph is the calendar. Peak flow arrives in the first half of June and the river is usually unfishable for three to four weeks. When the gauge starts to fall and the water turns from chocolate to green-grey, the cutthroat move back into the riffles and the season effectively begins. A dry year shifts everything two weeks early; a wet one shifts it two weeks late.
The insect plate
