Sirena

Sirena is the Tagalog and Spanish-derived word for a mermaid. Wikipedia says it is the general word that many ethnic groups in the Philippines use. A related Tagalog word, siyokoy, names a more fish-like water being. In stories, the sirena is a sea maiden who sings to fishermen, and her voice can draw them to the water.

Stories change from place to place. In Pangasinan, the Binalatongan mermaid is a sea queen who marries a mortal man, Maginoo Palasipas, and rules people for a time. Ilocano tales say that mermaids (serena) spread from the union of the first Serena and Litao, a water god. In Bikol, the magindara are known for beautiful voices and a cruel nature. A Cebuano folk tale, Ang Kataw, tells of a girl promised to a milkfish king in return for fish. Her parents later see her with a milkfish body.

Mermaid sightings around the world are sometimes explained by manatees, dugongs or seals. That is a general theory, and the sources do not tie it to the Philippines. The Kataw has its own entry.