Listen if your going to YSNP. You should fish Lower Slough creek. This is the water beloww the campground. It has more cutbows and their are bigger fish around down there.The first meadow above has the numbers and those fish are 14 to 16''. Also go to Tower Falls section of the Yellowstone River Good fishing to be had in the canyon. Access is the trail for the overlook to tower falls. There will be a sign saying that the trail is washed out @ the bottom. Its always washed out. its a pretty steep bank but doable. Just watch your step. Fish close up the Bank and you'll be able to access Tower Creek there. You may also get some run up fish from Hebgan Lake in the Madison. Big nymphs and streamers should let you know pretty quickly if their there. You may want to try Lewis river channel as well it's all Browns with an outside chance of a Lake trout.
Have a good time.