Fishing leeches and Woolly Buggers through the weedbeds is the most productive method. Dry-fly fishing can be excellent on Island Park Reservoir but it is often unpredictable. Morning hours are best, as big rainbows cruise the coves and weedbeds, rising to Callibaetis duns and spinners before the wind comes up. These fish can be a real handful on light tackle. The fish usually aren't selective about fly patterns.
Accurate casting is much more important.
I've also found that a small nymph, twitched in front of a cruising trout, is very effective. Inc. All rights reserved.