Mermaids are sometimes associated with perilous events such as floods, storms, shipwrecks, and drownings. In other folk traditions (or sometimes within the same traditions), they can be benevolent or beneficent, bestowing boons or falling in love with humans.
The male equivalent of the mermaid is the merman, also a familiar figure in folklore and heraldry. Although traditions about and sightings of mermen are less common than those of mermaids, they are generally assumed to co-exist with their female counterparts. The male and the female collectively are sometimes referred to as merfolk or merpeople.
The Western concept of mermaids as beautiful, seductive singers may have been influenced by the sirens of Greek mythology, which were originally half-birdlike, but came to be pictured as half-fishlike in the Christian era. Historical accounts of mermaids, such as those reported by Christopher Columbus during his exploration of the Caribbean, may have been sightings of manatees or similar aquatic mammals. While there is no evidence that mermaids exist outside folklore, reports of mermaid sightings continue to the present day.
In Zimbabwe mermaids are known as "njuzu". They are believed to be solitary and occupy one body of water. Individual njuzu may be benevolent or malicious. Angry njuzu may be blamed for unexpected misfortunes, such as bad weather or the sudden disappearance of people. Benevolent njuzu are thought to reside in peaceful lakes or rivers. If a person goes missing near such lakes or rivers, they may have been taken by the njuzu. To obtain the person's release, local elders will brew beer as a propitiatory offering, and ask the njuzu to return the person alive. Those seeking the person's release are not supposed to cry or shed tears. If the njuzu releases the person, they will become or be regarded as a n'anga, or traditional healer, with knowledge of herbs, medicinal plants, and cures.
9.4.9–11, Pliny the Elder, remarked that a triton (merman) was seen off the coast of Olisipo (present-day Lisbon, Portugal),[244] and it bore the physical appearance in accordance with common notion of the triton, according to a deputation from Lisbon who reported it to Emperor Tiberus. One nereid was sighted earlier on the same (Lisbon) coast. Pliny remarks that contrary to popular notion, the true nereids are not smooth-skinned in their human-like portions, but covered with scales all over the body.[247] Their mournful songs at death have also been heard by the coastal inhabitants. Also, multiple nereids had washed up on the shore according to the legatus/governor of Gaul, who informed the late Emperor Augustus about it in a letter.[244][249][246][ac]
16th century Swedish writer Olaus Magnus quotes the same passage from Pliny, and further notes that the nereid are said to utter "dismal moans (wailings) at the hour of her death", thus observing a connection to the legend of sea-nymphs[250] and the sister Fates whose clashing cymbals and flute tunes could be heard on shore.[251][252][250] Olaus in a later passage states that the nereids (tr. "mermaids") are known to "sing plaintively",[253][254] in general.[ad]
It has been conjectured that these carcasses of nereids washed up on shore were "presumably seals".