They will take nymphs that imitate caddis larvae in the mornings and then switch to adults by midafternoon when the number of hatching insects peak. Salmonflies migrate to the edge of the river to crawl out, hatch and make their first experimental flights. That is where you will find the fish, right on the banks gorging on the bounty of the giant Pteronarcys. This combination imitates the big Acronuria adults as well as a grasshopper, while the prince passes for the nymph. Once the big dry fly reaches the end of its drift, let it swing then strip it back in against the current.
Cutthroats seem especially prone to attacking the bright trudes on the move.
Wherever you find banks with both deep water and structure, you will find fish. During high water and strong flows look for trout in the inside bends where currents slow down. Once the water drops, you will find more fish against the banks on the outside bends. Anglers arriving by air can fly into Bozeman, Montana, which is 26 miles west of the Yellowstone River at Livingston. Cody, Wyoming, also has regular air service for visitors who would like to reach the Yellowstone River in Montana by driving through Yellowstone National Park, a distance of about 130 miles.