A Rusalka is a water spirit/nymph that originates in ancient pagan Slavic folklore. This myth is so compelling and eerie that Czech composer, Antonín Leopold Dvořák, created his opera, Rusalka, in her honor. Měsíčku na nebi hlubokém (Song to the Moon), is a world renowned aria.
In Russian and Ukrainian, Rusalka literally means mermaid, though these dark spirits are not like the Mermaids of Norse myth. For one, Ruslaki (plural), hang around lakes and rivers, not in the ocean. Also, they appear human mostly and do not have fishtails. Maybe you could say they are fresh water Mermaids. Ancient lore colors them as undead creatures with an appetite for luring men and children to their deaths. Like a siren, a Rusalka enchants men with her exquisite singing voice, luring him to the waters in which she hunts and lives, then she drowns him. It is said that the Rusalka also love children so much, that they will drown them as well, in order to keep them forever. In some cultures, the Rusalka myth is used to frighten children into staying away from potentially dangerous waters.
Of course, as is common with most pagan myths, with the coming of Christianity the Rusalka got a “lore-ish make over.” Rusalka kept their “undead” personage, but they became more like ghosts. They are said to be the eternally damned soul of a woman who committed suicide (usually in the body of water she haunts). Normally, the suicide was due to a betrayal by a lover. So yes, the Rusalka still hunt for men, luring them to their deaths at the bottom of their respective graves within the lake or river. These tormented souls roam the waters edges seeking their revenge upon unfaithful men. Because the ghost is usually to be seen in a long flowing white gown, the Rusalka have been nicknamed, “Lady in White.” Supposedly, Rožmberk castle, has their own resident “Lady in White/Rusalka.” She is said to haunt the castle and river outside it. The Castle sits alongside the River Vltava. A daughter of Duke Oldřich II, Perchta of the House of Rožmberk is believed to be this said ghost, as she had committed suicide there back in the 1400s.
In the hit TV series, Supernatural, a Rusalka/Lady in White makes her debut in the pilot episode. See clip: https://youtu.be/19ZETMYTr8Y
Měsíčku na nebi hlubokém (Song to the Moon) – Rusalka – Antonín Leopold Dvořák https://www.youtube.com/watch?v=uoPTh_q7GYs