I always wondered why the Chilliwack doesn't have summers?
Summer Steelhead seem to only occur where it is advantageous to return early in the season instead of in the winter. Generally, this is in places where the ideal spawning/rearing habitat is above a barrier that is only passable in spring freshet. The same is true of spring chinook - they generally travel further upstream than any other salmon, and they need the spring freshet to get there. Once there, they can chill (literally and figuratively) in the high mountain water until they are ready to spawn. The advantage for their offspring is that they are far upstream of the competition, and the water is cool year 'round (at least it used to be!). I recently read a study of the different run timings in the Skagit river for Chinook - the later they return, the further downriver they spawn. And I think Dave has said similar things about Vedder winter steelhead - the early returning fish and the ones that spawn the furthest upriver. If there were any natural summer run fish in the Chilliwack, I would imagine they would spawn in the upper Chilliwack River (above the lake) way upstream where almost no other fish venture. And if there are any native spring chinook left, I'd like to think that is where they are and that's why nobody ever sees them.