You have to think that there have been drought periods throughout history,  and for all but a tiny,  tiny portion of time,  the last 100 years,  there was no fish ladder on the falls at Oregon City.  It took a significant spring freshet or winter flood to put water in places that would allow steelhead to access the non tidal reaches of the Willamette.  And that was before dams.  It had to be a far different fishery then,  with resident cutthroat trout in a fluvial environment,  using the river or tributaries,  depending on the water flows and temperatures,  times of the year.  There would have been anadromous char once called Dolly Varden trout,  now limited to the fluvial new division of that species called Bull Trout.,  found above the dams in small numbers.  12 significant dams,  many without fish ladders,  have compromised the Willamette basin.  Even the chinook are Wind River origin hatchery strain,  with "wild" fish of indistinct genetics.  Man,  not drought,  is the problem.