Popular culture outside Slavic-speaking Europe has flattened the rusalka into a kind of Slavic mermaid, most visibly through Dvorak's opera Rusalka, in which the title character trades her voice for legs to pursue a human prince, a plot borrowed more from Hans Christian Andersen's The Little Mermaid than from Slavic folk sources. Traditional rusalki are not fish-tailed and are not consistently aquatic in the way a mermaid is; many accounts have her walking freely onto land, particularly during Rusalka Week, and her defining feature across most tellings is her manner of death and her unquiet state rather than any specific anatomy. The mermaid comparison is convenient shorthand but flattens exactly the ambiguity, part ghost, part nature spirit, part fertility figure, that makes the rusalka distinct within Slavic belief.
Within this atlas's own Water Spirits heading, the rusalka sits alongside the Scottish and Irish kelpie, a shapeshifting water-horse that drowns riders rather than luring them with song, and the comparison is useful for what it clarifies by contrast: the kelpie is an animal spirit defined by predation and shapeshifting, while the rusalka, in most of her tellings, is a human dead, defined by grief, injustice, or unfinished life as much as by any threat she poses to the living. Grouping the two under one heading reflects a shared domain, fresh water, rather than a shared origin or nature, and the atlas records that distinction rather than letting the heading imply an equivalence neither tradition claims.