Last Fall I fished the Big Thompson River around the Fern Lake Trailhead for a couple of hours.  Although the area around the Cub Lake Trailhead was crowded with guided trips there were no other anglers on the river upstream. The water was low now so crossing the river was not a problem. The brook trout and browns were actively feeding as the temperatures cool and the leaves turn. All fish caught and released using a flying ant pattern. Keep this as an option when the water levels cooperate.