Much like sirens, mermaids would sometimes sing to sailors and enchant them, distracting them from their work and causing them to walk off the deck or cause shipwrecks. Other stories would have them squeeze the life out of drowning men while trying to rescue them. They are also said to take them down to their underwater kingdoms. In Hans Christian Andersen's The Little Mermaid it is said that they forget that humans cannot breathe underwater, while others say they drown men out of spite.

The sirens of Greek mythology are sometimes portrayed in later folklore as mermaid-like; in fact, some languages (such as the Maltese word 'sirena') use the same word for both bird and fish creatures. Other related types of mythical or legendary creature are water fairies (e.g. various water nymphs) and selkies, animals that can transform themselves from seals to humans.

Ancient Near East

A popular Greek legend has Alexander the Great's sister, Thessalonike, turn into a mermaid after she died. She lived, it was said, in the Aegean and when sailors would encounter her, she would ask them only one question: "Is Alexander the king alive?" (Greek: Ζει ο βασιλιάς Αλέξανδρος;), to which the correct answer would be "He lives and still rules" (Greek: Ζει και βασιλεύει). Any other answer would spur her into a rage, where she transformed into a Gorgon and meant doom for the ship and every sailor onboard.

Lucian of Samosata in Syria (2nd century AD) in De Dea Syria ("Concerning the Syrian Goddess") wrote of the Syrian temples he had visited:

"Among them - Now that is the traditional story among them concerning the temple. But other men swear that Semiramis of Babylonia, whose deeds are many in Asia, also founded this site, and not for Hera Atargatis but for her own Mother, whose name was Derketo"

"I saw the likeness of Derketo in Phoenicia, a strange marvel. It is woman for half its length, but the other half, from thighs to feet, stretched out in a fish's tail. But the image in the Holy City is entirely a woman, and the grounds for their account are not very clear. They consider fishes to be sacred, and they never eat them; and though they eat all other fowls, they do not eat the dove, for she is holy so they believe. And these things are done, they believe, because of Derketo and Semiramis, the first because Derketo has the shape of a fish, and the other because ultimately Semiramis turned into a dove. Well, I may grant that the temple was a work of Semiramis perhaps; but that it belongs to Derketo I do not believe in any way. For among the Egyptians, some people do not eat fish, and that is not done to honor Derketo."