Mermaids are considered humanoids that are half human half fish that live in water, but can also come to the waters surface. In folklore, Mermaids are mystical creatures that are usually associated as being bad luck or tricksters. They have the ability of seducing fishermen at sea and usually lure them to their death by way of drowning. However, other reports differ claiming that Mermaids are good and help people lost at sea.
In GTA San Andreas, rumors of Mermaids and Sharks began to surface a few years after the game was released. It took several years to prove Sharks existed in the game, but the rumors of Mermaids fell into obscurity and were practically forgotten. A few reports claim that Mermaids are off the coast of Los Santos' beach where the lowrider mission and dance parties take place. This could be associated with the Underwater World myth. However, believers insist their encounter was with an actual Mermaid.
There are a few mods on the internet for Mermaids and even fewer images, let alone videos of the alleged creature. At this point evidence pointing to the Mermaids' existence is weak, due, in part, to the huge lack of research on the subject. Given the fact the Shark myth lingered for years before being proven, it is possible that the Mermaids could be real.