I recall 2 things when thinking of the San Juan: Big fish, small flies. It's mostly a midge fishery with plenty of bugs. The "San Juan Shuffle" is the act of "accidentally" dragging one's feet through the gravel bars at top of runs. It stirs up nymphs akin to chumming. Not suggesting it, just saying I learned about it from some locals. I think it's generally looked down upon and may even be against regulations.