I'm sure when you think of a mermaid you picture what we've been indoctrinated to imagine - a beautiful blonde woman with long flowing hair, much like the one in this photo.
Cape Town, well, rather Swellendam (a small town 225Km outside of Cape Town) has it's own mermaid legend - that of the Kaaiman. From what I can tell sightings are extermely infrequent, with the last reported one being in 2008. The Kaaiman is apparantly a white woman with long black hair, red eyes, and a fish-like lower half. Read this story on Monstropedia for details on the 2008 sighting.