Hello

Just got back a couple weeks ago from a week in Yellowstone. You should consider fishing the following:

Slough Creek in the first meadow BUT also be sure you fish the boulder field from where Slough leaves the meadown and plunges down to the slower water above Slough Campground. That boulderfield is LOADED with nice Rainbows and Cutt's. A Hopper with a beadhead (fast sinking) nymph will catch you a mess in the boulder field. Fish up in the Meadow were taking well tied hoppers and CDC ants.

Grebe Lake was fishing exceptionally well while I was there. Rainbows and Greyling were crushing a mix of dries (CDC Caddis, emergers, Adams Parachute), wets like Chronomids and Hare's ears.

Do not waste your time on the Yellowstone in the park as it's dead. FLoating the Yellowstone below the Yankee Jim Canyon is awesome though with lots of big fish.

Also wandering outside the park to the MAdison below Quake LAke near the 3 Dollar Bridge has been great. LOTS of big fish here on nymphs during the day and dries in the evening.

Hope this helps a bit.