Gardiner is centrally located near some of the best fly-fishing in the world. The Yellowstone River, which flows through town, and the various rivers inside Yellowstone National Park, offer ample opportunities for fly-fishing. For more information, visit Parks Fly Shop or The Flying Pig Campstore.
For lake fishing, head up to Daily Lake (just a 45 minute drive north of Gardiner), down to Yellowstone Lake in the park (2 hour drive from Gardiner), or hike up to Knox Lake in the Absaroka Beartooth Wilderness (trailhead in Jardine). Fishing permits are required in Montana and in the park.