The Water-wraith is a specie of Lesser Faeries that lives in Prythian. Feyre meets them for the first time in A Court of Mist and Fury, during the Tithe, when one of them begs Tamlin not to punish her and her sisters because they can't pay the Tithe. In fact, their lake is empty of fishes and they are starving, because water wraiths never stop eating. Tamlin refuses and tells her she has three days to collect her payment. So Feyre goes to the Water-wraith and, out of pity, while remembering when she also suffered like that, gives the water-wraith her jewelry so that she can use them as payment. The water-wraith thanks Feyre and it tells her that she and her sisters are now in debt. Later in the book when Feyre and Armen are drowning in their attempt to steal the Book of Breathings they are saved by a group of Water-wraiths as a payment for the debt they had towards Feyre.
Water-wraiths are slender and gray-skinned. They wear no clothes. They have long, dark hair that hangs limp over their breasts, a sharp angular face and massive eyes that are wholly black. When they move, the light shimmer on their iridescent skin. Their teeth are as sharp and jagged as a pike’s. They have webbed fingers with jagged nails and webbed, clawed feets. Their nose is little more than two slits, and delicate gills flare beneath their ears. Their skin is cold and clammy.