The Madison is fishing best below Hebgen Dam and downstream to Earthquake Lake . You may see midges in the Raynolds or $3 Bridge areas. Have a Zelon or Skittering Midge #20-22 with you when you go. Nymphing will be your best bet here and I would suggest Zebra Midges #18-20, Micro Mayflies #18-20, brown or Black rubber legs #8-10 and yes, a San Juan worm will be productive. Below the dam is best with egg patterns, Micro-Madison Midge nymphs trailed behind a brown or black rubber legged stone and an olive sculpin.