An informative summary report on adult and juvenile passage facilities and the wide range of success or not of doing so is in this link. It mentions that for 77 days during juvenile outmigration power generation is shut off at Wynoochee Dam and juveniles pass downstream through outlet pipes at the dam. Doesn't say how well this works though.


Generally getting adults upstream has a lot better survival than getting the juveniles downstream.

https://link.springer.com/article/10.1007/s11160-020-09627-7