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.
Here is a legend about a sirena from one of the islands in Zambales, Philippines.