In Slavic mythology, a rusalka is a female ghost, water nymph, succubus, or mermaid-like demon that dwelt in a waterway. In most versions, the rusalka is an unquiet dead being, associated with the “unclean force”. People who die violently and before their time, such as young women who commit suicide because they have been jilted by their lovers, or unmarried women who are pregnant, must live out their designated time on earth as a spirit.
According to most traditions, the rusalki were fish-women, who lived at the bottom of rivers. In the middle of the night, they would walk out to the bank and dance in meadows. If they saw handsome men, they would fascinate them with songs and dancing, mesmerize them, then lead them away to the river floor to their death. (x)