At least in Oregon, there is a distinction between "fly only" and "fly fishing only." On waters that fall under the former regulation, conventional gear is allowed so long as a fly is used. Under the latter scheme, a fly rod, fly reel, and fly line is required.

Of course here in Oregon, the same kind of wonderfully inclusive and egalitarian fellows who stay stuff like "it's easier than using a baitcaster," while completely ignoring the fact that THEY aren't in a wheelchair, just harass the Game Commission until it makes the "fly only" waters de facto "fly fishing only" by insisting on banning weighted flies.