The lower Yellowstone river begins at the outlet of Yellowstone Lake. After passing through Hayden meadows, it drops over the Upper and Lower Yellowstone Falls at the head of the Grand Canyon Of The Yellowstone within the confines of the park. After passing through the Black Canyon of the Yellowstone downstream of the Grand Canyon, the river flows northward into Montana exiting the park at Gardiner.
Inside Yellowstone National Park is some of the most gorgeous flat water fishing for pure Yellowstone cutthroats you'll experience anywhere. A portion of this stretch (through Hayden Valley) is closed all year, but the rest is easily accessible and easily wadable. No floating is allowed. Wonderful hatches occur just after the opener, on July 15. Pale Morning Duns, Green Drakes, Gray Drakes, caddis and even salmonflies are found at that time. The river can be crowded at popular access points like Buffalo Ford, but if you hike a bit, there are many good spots where you can get away from the crowds.
The canyon reaches inside Yellowstone National Park are accessible only by hiking or horseback. This is some terrific fishing at times, especially during the salmonfly hatch in early to mid-July. Good access points are at Canyon Village, Tower, and Gardiner with a couple of other trailhead access points in between. If you are in good shape and like to combine some hiking and fishing, this is great water to explore. The scenery is magnificent. The river here is usually quite swift, with sheer canyon walls in spots. Wading can be dangerous in these sections, so be careful. The payoff are big fat cutthroats and some very nice rainbows. Below Knowles Falls, about four miles (6 km) upstream from Gardiner, you'll find browns and whitefish in addition to the rainbows and cutthroat trout.
All whitefish and cutthroat trout caught in the Yellowstone river must be released. Five rainbow and/or brown trout may be harvested from the lower Yellowstone river.