Water Genasi, who sometimes call themselves Sea Kings, are patient and independent, used to solving problems on their own and not afraid to take a lot of time in doing so. They can be fierce and destructive like terrible storms, or as calm and placid as a gentle pool, despite the fierce emotions that might lie beneath the surface. Their Elemental forebear usually has little interest in them, so they are often raised by other creatures of water.
Water genasi look human except for some distinguishing feature - clammy or slightly scaled skin, blue-green hair, large black eyes, or webbed hands, for example.
Sources: Planewalker's Handbook, Races of Faerun, Monsters of Faerun