When the prince introduces his "little mermaid" to the princess who found him on the beach, he remarks on how similar they are. In reality, the actresses portraying them (Miroslava and Libuse Safránková) are sisters.
One of two adaptations of Hans Christian Andersen's faerie tale released in 1976. The other is The Little Mermaid (1976).
The Italian poster features the protagonist as a blonde and the picture of a more traditional mermaid, which was dropped in the film and is mocked by the characters in the story.