Fly-fishing has its sacred waters the world over. Yellowstone National Park claims some of the craft's most storied destinations. Casting in the Firehole River is like going back in time to when bison roamed nearly every meadow in the West. Restored to their natal streams after near extinction, native Arctic grayling can once again be plucked from icy water at the foot of breathtaking waterfalls. Meanwhile, a daylong hike into true wild country rewards...