Smaller backcountry streams demand bigger flies. Why? Food is scarce in cold, clean water and high-country fish want a feast—not a snack. The perfect sizes and shapes vary based on region, season, waterway, and time of day, so ask local fly shops for recommendations on specific hatch-matching styles. For a sure thing, bring basic stimulator patterns ranging from size 10 to 16. The Parachute Adams and Royal Wulff draw strikes across the country.