The Gardner River begins in the mountains west of Mammoth, at Joseph Peak. The upper sections of the Gardner River, upstream from the Mammoth-Tower bridge near Mammoth Hot Springs, offers only limited fishing possibilities, with small brook trout the primary resident.
The best fly fishing on the Gardner River will be found in its lower stretches, just upstream from the Yellowstone Park Boundary. The road between Gardner and Mammoth Hot Springs provides easy access for much of this section, while a hiking trail follows the river into Gardner Canyon.
The terrain in this section of the park is noticeably different than found elsewhere in Yellowstone. The lower Gardner River area is very arid, with trees only found on the upper mountains. The valley itself is quite arid with extensive meadows and sagebrush.
The Gardner River upstream from Gardner flows quickly and has extensive smaller rapids. Lots of runs, riffles and some pools are found on the lower Gardner River. Rainbow and brown trout are both found in the lower river, averaging around 12 inches, although occasional large fish are taken.
The Gardner River generally runs clear before other nearby rivers. As a result, productive dry fly fishing can occur in June if favorable conditions occur. Popular dry flies for the lower Gardner River include the Elk Hair Caddis and the Parachute Adams (sized 14-18). Beginning in July and lasting through September, the Gardner River, as elsewhere in many of Yellowstone’s rivers, is an excellent place for hopper and beetle imitations, sized 4-10.
Fly fishing pressure on the Gardner River in Yellowstone National Park is quite low compared to other major rivers in the park. Solitude is easily found just off the road or by hiking a short distance up the many trails that parallel the river. It should be noted that the lower stretches of the river has a quick current and lots of slippery rocks. While the river is not very deep or wide once spring run-off ends, the fast current and slippery rocks can make wade fishing and good presentation a challenge.