Idaho has 5 native trout eligible for the Challenge: Redband, Bull, Westlslope cutthroat, Yellowstone cutthroat, and Bonneville cutthroat trout. Now that rivers are down to low summer flows, late summer and early fall is a great time to seek native trout. Using tools like the Idaho Fishing Planner or the Trout Challenge Maps is a good first step to finding the species you are after. Cutthroat and Redband are easier to catch and are widely distributed across the state. Bull Trout often migrate long distances and are less common, so be prepared to hunt for them.  It's been a hot summer, so I recommend fishing higher elevations, and focus on fishing early or late in the day when water temperatures are cooler and fish are biting best.