My home river, the Clackamas, Didn't have fish passage to the upper river for about 20 years in the mid 20th century. After fish ladders were put in at reliscencing, the wild steelhead were returning in the thousands within about 10 or 15 years (can't remember). Had the dams come out, it's reasonable to think the return would've been better since the ladders have been shown to dramaticly slow the adult fish down and kill smolts. I don't know how big the fish used to be, but the Clack does produce wild 20 pounders and I enjoyed a 17 pound wild fish there last year.