A gorgeous trout from Armstrong Spring Creek in Montana's Paradise Valley.. photo by Brant Oswald When cold weather rolls into the mountains, many rivers freeze or become very difficult to wade. Spring creeks, however, usually maintain a near-constant water temperature throughout the year, which makes them prime winter fisheries. In the early 90s, I guided at Hubbard's Yellowstone Lodge in Paradise Valley, Montana, where I got the chance to fish all three famous spring creeks there. But it wasn't until two years ago that I got the opportunity to experience a spring creek in winter. On a day when the mercury never got above 20 degrees, we were able to cast to feeding fish for most of the day on Armstrong Spring Creek. It wasn't comfortable, . . .