Dry fly fishing: 1
In fly fishing, “dry fly” is a general term describing a type of artificial fly representing insects in their mature or adult life stage. When an insect hatches to its adult form, it is commonly found resting on the water’s surface before it takes flight and eventually mates or crawls to the safety and shelter of the riverbank. It is during this resting or migration period that hungry and opportunistic trout actively rise to the surface to feed on these hatched insects.
Compared to the larval or nymph stage, an insect's adult life is generally much shorter. For this reason trout must catch the insects during the relatively brief window of their emergence from the nymphal shuck, while the fly rests on the surface film, or makes its way to shore. This is the origin of the fly fishing concept of "fishing a hatch."
Dry flies are fished either on the surface of the water or just beneath the surface film. An effective dry fly presentation requires the fly to remain dry, and not waterlogged; thus giving the category of fly its name. Important aspects of dry fly design are: the ability to shed water during false casting; the ability to ride high on the surface film; and its ability to be visible in many different kinds of water. Unlike nymphs in fly fishing, you do not use extra weight with dry flies, since they must be as buoyant as possible in a range of water conditions.