My guess is the small tributary feeder streams will be very low this summer. If you have a DIY float trip planned and are landing in a headwater lake, be advised that getting boats down these small streams might be very difficult. Your air taxi operator should be able to suggest other options such as landing on a gravel bar part way down the river.
The medium sized and larger rivers will still be navigable and should fish fairly well. Side channels and braids in rivers may be low or non existent if the summer is dry. This will push all the fish into the main river channel. This does consolidate fish but if the river gets a lot of angler pressure it also puts all the fishermen in one channel, too.
All this being said, if it is a rainy summer then the predictions go out the window! In any event, the salmon will return and the Dollies and rainbow trout will be there to greet them.