Ill consider the question searching for fish, As opposed to searching for a correct fly.. I fish a large river ,Missouri, and use long distance casts, fish huge amounts of water with spey rod from shore, or boat with 6wt single hander, and heavy sink tips. .. During the day, bright flys work best, like a little trout, or spruce fly, and in the evening dark streamers,buggers, work best.. Fishing, and refishing large amounts of productive water has shown me how much fish can move thier feeding places in a short time (or be put down by fishermen constantly beating the water in a single area).. Watching surface hatches and swallows feedding over the water is a big help finding the best feeding/fishing areas. dave..