As GregM wrote, tenkara "line" is analogous to fly fishing "leader." The rods are so supple that many of them will easily cast fifteen feet of 0X fluorocarbon tippet material, to which is attached 3' of 5X tippet and an unweighted soft hackle fly. Just like fly rods, tenkara rods cast the weight of the line, even though the line might weigh only 10-15 grains, as opposed to the 60 grains of a 1-weight fly line. Most tenkara rods would easily cast a 12 to 15' knotless tapered fly fishing leader (no fly line, just the leader). In fact, both in Japan and the US, some tenkara anglers use just that, a knotless tapered leader of 3.5, 4 or 4.5 meters in length to which a Hi-Vis dye was added in the manufacturing process so they can watch the "line" for indication of a strike. Even a 1 weight fly line is too heavy - or at least much heavier than necessary.

Why do the state regulations require 25' of conventional fly line? What were they trying to exclude? In tenkara fishing, just as with "conventional" fly fishing, an unweighted fly is propelled by casting the weight of the line (even though the line weight is very small). To me, that seems much more "conventional" than say, short line Czech nymphing, in which an angler lobs a couple heavily weighted nymphs with perhaps no more than a foot of fly line beyond the tip guide. Czech nymphing is legal in fly fishing only waters. An angler may in fact have 90' of fly line on his reel, but none of it is ever used. If it never leaves the real, why do the regulations require that he have it?

The real question, though, is whether the regulations are written to preserve the fishery or to preserve someone's idea of traditional fly fishing. Tenkara is no more damaging to the fishery than conventional fly fishing. Same fly, same tippet strength, (and therefore the same pressure that can be applied to landing the fish). With respect to tradition, tenkara is just the Japanese word for the fly fishing practiced by Izaak Walton, Charles Cotton and Dame Juliana Berners. If anyone thinks that Dame Juliana Berners, were she alive today, should not be allowed to fish in Washington's Fly Fishing Only waters, I would love to hear him try to make that case.