In my fly-tying room is a shelf full of books devoted to trout fishing, and I've read them all. With the exception of one or two, Moving Water has more information to help make you a better trout fisherman than any of the others. You'll have to read it and reread it many times to fully absorb its contents so you can use it in pursuit of trout wherever there is current, be it a tiny brook, a tumbling mountain creek, a meandering limestone stream, or a large river.
-- Lefty Kreh, fly fishing legend and author of numerous books, including Casting with Lefty Kreh, Fly-Casting Fundamentals, and 101 Fish