Slavic testimony about the rusalka is not uniform, and the differences are not incidental. In the eastern and southern traditions recorded across Russia, Ukraine and Belarus, the rusalka is most consistently the unquiet dead, a young woman whose death was somehow wrong or premature, unbaptized infants and drowned girls being the two most commonly cited origins, condemned to haunt the water where she died until some ritual or accident releases her. In parts of the western Slavic record the figure blurs into a broader, less individualized nature spirit associated with fields and forests as much as water, closer to a fertility figure than a restless ghost, which is why some ethnographers resist translating rusalka simply as "water spirit" at all.
The best-documented ritual context for the belief is Rusalka Week, Rusalnaya nedelya, a period in late spring or early summer, historically tied to the Slavic agricultural calendar and later folded into the Orthodox calendar around Pentecost, during which rusalki were believed to leave the water and wander fields and woods, and during which villagers observed specific taboos, avoiding swimming and certain fieldwork, and performing rites to send the spirits back to the water at the week's end. The seasonal, calendrical dimension of the belief, well attested in nineteenth and early twentieth-century ethnographic collection, sits awkwardly with the purely sinister, purely nocturnal image the rusalka usually carries in later popular retellings, and is a large part of why scholars treat the figure as older and more agrarian in origin than the drowned-bride story alone would suggest.