Rusalka (plural: rusalky or rusalki) is a female water demon in Slavic mythology and folk culture. First traces of this name come from the 16th century when rusalka replaced víla in Eastern Slavic culture. Rusalka and víla have both long and often red hair, however, rusalka’s hair would cause floods when combed out. Also unlike víla rusalka would rather harm people than help them. In the middle of the night, they would walk out to the bank and dance together in meadows. If they saw handsome men, they would fascinate them with songs and dancing, mesmerise them, then lead them away to the river floor (or swamp) to their death.
Holiday rusaje was dedicated to these beings together with reminiscence of the dead. Probably under influence of this feast day emerged the idea of rusalkas as souls of girls who died early, often by their own hands.