Hi Plug, there are "smolt passage tubes" in the dam that are supposed to let downstream migrants out. This is after they are scraped out of the way of the turbine intakes with an Eicher screen. From working on this project in the 70's, right after the abortion was built, I can tell you that they do not work well at all and that few smolts survive the trip.

I suspect the slabs that find their way into the holding pen, for truckin around the dam, wind up there because the dam, among other things, has prevented gravel recruitment and has turned spawning beds into boulder fields for a mile downstream. These poor guys have no more gravel to spawn in and so are going to get the chance upstream of the dam. Fat chance if you ask me.