Nymphs and submerged are artificial...

Wet Flies & Nymphs BL

Nymphs and submerged are artificial flies that, unlike dry flies, work under the surface of the water. Because of their characteristic these artificial flies do not sink much and are ideal to go in search of fish in midwater while it is concentrated to eat the small nymphs that are emerging from the bottom of the river. They are also very effective in shallow and slow water or in all those situations where you have to fish under the surface of the water but without necessarily having to reach the bottom.

Vogel