In Greek mythology, the Nereids ( ; , sg. ) are sea nymphs (female spirits of sea waters), the 50 daughters of Nereus and Doris, sister to Nerites. They often accompany Poseidon, the god of the sea, and can be friendly and helpful to sailors fighting perilous storms, as the Argonauts find the Golden Fleece.

In Greek mythology and, later, Roman mythology, the Oceanids (; ) are sea nymphs who were the three thousand daughters of the Titans Oceanus and Tethys. Each was the patroness of a particular spring, river, sea, lake, pond, pasture, flower or cloud. Some of them, such as Calypso, Clymene, Asia, Electra/Ozomene, were closely associated with the Titan gods or personified abstract concepts (Tyche, Peitho).