The sirena is one of the merfolks in Philippine folklore. She is depicted as half-woman from the torso upward and half-fish downward. Along with other sea creatures like kataw and syokoy, asirena has dominion over bodies of water including seas, rivers, and gulfs.
Here is a legend about a sirena from the province of Ilocos.
The people of Laoag say that in that tree there lived a super-human being, which they call Sirena. Many of them say that Sirena has the appearance of a woman, while others say that half of her body is fish and the other half is woman. Many interesting stories spread about Sirena.
Here is one of them:
There was nobody else in the area except the woman and her child. So, Sirena made up her mind to go to the woman and ask her if she can have that woman's child in her care. Sirena then approached the woman and said, “Woman, give me your son, and I will feed him, teach him, make him rich, and then return him to you again.” The poor woman hesitated for a moment, but afterwards she yielded to the wishes of Sirena. She then took the child with her, and the woman returned to her home with mingled feelings of sadness and happiness.
The child accompanied Sirena in her usual strolls along the river. She showed him her deposits of money and other valuable properties. She taught him many things, especially how to cure different types of sickness. They lived in the same house and ate the same food.
Days, weeks, months and years passed by and the little child had grown into manhood. He already acquired part of Sirena's wisdom. Remembering her promises to the man's mother, Sirena then took some of her treasures and gave them to him as present.
One day, the woman went again to the river. Sirena went out to meet her and then returned her son to her. The woman was filled with joy in her heart.
She thanked Sirena for her kindness and for taking care of his child.
The mother and son then departed.
Cadamba, C. (1915). Sirena. Manila, Philippines: Iloko Paper Nc. 26; Folklore 2418.