Sirenuca

In Cantabrian popular tradition the Sirenuca is narrated as a beautiful but disobedient and spoiled young woman whose vice was climbing the most dangerous cliffs of Castro Urdiales to sing with the waves. The tale frames her change as a moralized metamorphosis: because of her persistent behavior at the sea margin she was transformed into a water nymph. Sources present this metamorphosis as the origin of the Sirenuca rather than as the appearance of a separate, preexisting class of being.

Sources label the Sirenuca as a 'Little Mermaid' and as a 'water nymph.' Before transformation she is described in the tradition as a beautiful young lady; after the metamorphosis she is referred to generically as a water nymph. The available texts provide no standardized iconography or specific anatomical details (such as fins, tail, or precise size) beyond these descriptors.

The tradition emphasizes her vocal practice: she climbed the cliffs to 'sing with the waves,' and the story links this singing and her presence at the sea margin to her transformation into a water nymph. The sources do not attribute other specific powers, such as enchantment, luring, healing, or harming; no further habitual interactions with humans are recorded in the provided material.