

If you mean “fly 3” as a third fly option for trout, the strongest choices here are the dry-fly and nymph patterns. The three Harrop CDC flies cover the most common technical surface situations: Harrop's CDC Biot Dun PMD - Solitude - Mayfly Dry Fly for PMD hatches, Harrop's CDC Biot Emerger BWO - Solitude - Mayfly Dry Fly for BWOs in the film, and Harrop's CDC Biot Dun Trico - Solitude - Mayfly Dry Fly for tiny, selective surface feeding. If you need a subsurface option, Micro Pat's Rubber Legs is a good trout nymph for getting down fast in clear or pressured water.
Switch away from dries if trout stop rising, the hatch is over, or fish are feeding deeper. In that case, a nymph like Micro Pat's Rubber Legs is the better move. If you meant saltwater or bass instead of trout, say so and I’ll narrow it to the right fly type.
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