Lots of deep water Smallies move into river systems to spawn. Knowing the fish, it's spawning temps, it's preferred structure, it's preferred spawning substrate, it preferred food, how it deals with sunlight, does it school, how it hunts, when it hunts, how weather affects it's daily routine, etc etc. Most fly fishing books I've got with the exception of a few just don't have that much detailed info on the species and its prey.