Ariel wata yarinya ce mai shekaru 16 wacce ba ta gamsu da rayuwar karkashin ruwa a masarautar Atlantica kuma duniyar mutane ta burge ta. Tare da abokinta mafi kyau Flounder, Ariel tana tattara kayan tarihi na mutane a cikin kogon ta kuma galibi tana zuwa saman teku don ziyartar Scuttle, wani seagull wanda ke ba da cikakken ilimin al'adun ɗan adam. Ta yi watsi da gargaɗin mahaifinta Sarki Triton, mai mulkin Atlantica, da Sebastian, wani crab wanda ke aiki a matsayin mai ba da shawara na Triton da kuma mawaƙin kotu, cewa an hana hulɗa tsakanin mutane da mutane. Tambaya: Shekaru nawa Ariel?
'Yar shekara 16