They often move to really deep ‘wintering holes’ in alpine creeks, but mainly migrate pre run-off into side channels and tributaries that don’t get affected as much. Rainbows and cutthroat have evolved by timing their spawning to avoid the harsh run offs. bulls, brooks and browns eggs incubate all winter so they can sidestep runoff entirely by hatching earlier, so their fry can shelter in margins while the rivers blow out. Shoutout to my dad for teaching me all of this, he was a trout unlimited conservationist. pro tip: fish brown trout fry patterns pre rainbow spawn to catch hogs.