Selway-Bitterroot Wilderness Fly-Fishing (Idaho - Montana) is located near Elk City, Idaho. The trail is primarily used for fly fishing and is accessible from June until November.
Great trail for backpacking, even if it's your first time. Took my girlfriend for her first backpacking trip along this route, and she loved it. The grade is tolerable throughout the hike, as it follows the river the entire way. You can camp along the river in a few areas with sandy beaches (if you dare). Nothing better than the wild and scenic area along the Selway! You'll likely see kayakers as you hike, as this is area is world renowned for its white water. Most adventures will kayak this section of the river.