There is a new map book out there that shows all relavent put in's and take-out's on Washington Rivers. It doesn't help much for how fishy the water is....species of fish etc., but it might help to save you from over-committing float length and floating in to the dark.
I've heard some people do that from time to time
As for a book that is comprehensive and covers species and productive floats...you might be on your own and have to do things the old fashion way and learn for yourself (with help from the community of course).
Although aimed at rafts, canoes and kayaks not drift boats specifically, pick up a copy of "A Guide to the Whitewater Rivers of Washington". It is a fairly comprensive book of most of the navigable rivers in the state, including all the ones you'd normally float to fish. If you are floating rivers in any kind of boat, you should have something like this.
It includes details on class of rapids (at which flows), lenght and times of floats, rapids, hazards, river gages, map references, along with river descriptions, put-ins, take-outs, etc. This book may be a lifesafer and help you avoid trouble: unknown hazards, too long a float, too heavy flow, etc. If you are floating a river in any kind of watercraft - pontoon, raft, driftboat - it is critical to remember you are first and foremost running a river and should be prepared as such. People get into trouble fast when they think they are merely fishing and the boat is just something necessary to get them to good holes.
Be safe - 2 drownings this month just on the Yak...
Sue mentioned a great book. Think I still have an old copy of that one laying around. Very accurate. Luckily, has some pretty mild rivers as well in it. Only big problem with that book, most of the rivers mentioned are the sections usually not fished (at least by boat). Though some are (some on the Duc, etc).
If I didn't have stuff packed up for my move, I'd find the name of the book I have. It's a steelheader's guide, but lists all the big rivers (with named launches and nautical miles) throughout. It's an older publication, but still extremely accurate (and have one just for the OP as well).
There's another book as well, just can't seem to remember the name of it. Think it's an Amato publication. Has salmon/steelhead rivers listed in it.