In Slavic folklore, the rusalka is a typically feminine entity, often malicious toward mankind and frequently associated with water, with counterparts in other parts of Europe, such as the French Melusine and the Germanic Nixie. Folklorists have proposed a variety of origins for the entity, including that they may originally stem from Slavic paganism, where they may have been seen as benevolent spirits. Rusalki appear in a variety of media in modern popular culture, particularly in Slavic language-speaking countries, where they frequently resemble the concept of the mermaid.

The Nixie, Nixy, Nix, Näcken, Nicor, Nøkk, or Nøkken are humanoid, and often shapeshifting water spirits in Germanic mythology and folklore.