Wet flies can be fished as a team or you can use wet flies as part of a washing line rig using a buoyant fly to lift the rig from a lake bottom or even with a buoyant dry fly like an elk hair caddis or even a foam terrestrial fly with the wet flies suspended at a fixed depth on droppers drifting with the streams current.
What is A Wet Fly?
A wet fly is designed to be fished below the water's surface. Wet flies vary from traditional wet flies used for over a hundred years to modern using flashabou type and other bright modern materials. A wet fly can be quite large bodied or extremely slim like Blank Buster Spiders, Northern spiders which are tied very sparcely to imitate an emerger with one and a half turns of hackle imitating the emerging legs on an emerging fly. The success of the wet fly often depends far more on its action than it resembling a specific insect and matching a hatch / nymph. When fish are on the feed the actual pattern is generally not important, but when the fish are preoccupied or need tempting the angler must use ingenuity to discover what the fish are feeding on and what color they are taking. When fishing wet flies, it is important to remember that the higher the wave on the water the higher the fly hook size can be, but still take into account the brightness and clarity of the water.
Trout do see subsurface insects with wings. Some flies begin to hatch below the water surface. Some up-winged flies swim or crawl beneath the surface as adult spinners in order to lay egg. Often duns & spinners are swamped by the current and forced under the water surface. Emerging duns that have been unable to get rid of their nymphal case or at the time of emerging are drowned when they float under rough water that is flowing over a large rock or ledge are also hunted by the fish. The trout on purpose lurk in slack water near eddies and small plunge pools to look out for these type of snacks. Clearly a trout does see winged insects under the surface at certain times of the year so be prepared with a selection of different colored wet flies for when the fish are not taking from the surface.
Fishing the Wet Fly
Probably the most common way to fish a soft-hackle wet fly is to cast it across and slightly downstream, letting it sink and then swing in the current, rising with the tightening line much as a natural rises to the surface before hatching. It's on this rise that fish usually strike. Another productive method is to cast the fly upstream on a short cast and then let it dead-drift back to you just under the surface (or, if tied on a light-wire hook, in the surface film). On lakes and ponds a soft hackle fly cast in front of a cruising trout and then twitched slightly can be absolutely deadly. Many wet fly anglers, especially in Europe, favor fishing two or three of these flies (of different colors and sizes) at a time.