The maiden who drowns herself in the Kalevala is Aino.
Aino is the younger sister of Joukahainen, the boastful young man who challenges Väinämöinen to a contest of magical knowledge and song. After losing, Joukahainen promises Aino as a bride to save his own life. Aino is distressed because she does not want to marry the much older Väinämöinen.
Her story appears early in the epic and is one of its most tragic episodes. Aino rejects the marriage arrangement, runs into the forest, and eventually goes to the sea. She drowns herself rather than accept a life chosen for her. In later episodes, Väinämöinen encounters a mysterious fish that is revealed to be Aino in transformed form, but he fails to recognize her before she escapes.
Aino is not one of the epic’s gods or supernatural rulers. Päivä is associated with the sun, Mielikki with the forest, and Louhi is the powerful mistress of Pohjola. Their roles can make the options seem mythologically plausible, but Aino is the specific maiden linked to the drowning episode.