In the area of Gosauzwang (Gosaumühle, Gosau-Mill) which is located at the Hallstätter Lake in Upper Austria there are quite a few houses that are pretty old.
'Pretty old' means: Houses that still 'stand' and where people live in and which were built in the 16th century. Besides there are remains from the times when the Celts and the Romans lived and worked here.

At one of these houses I found this painting of a mermaid (in German you call them also 'Nixen' or 'SeeJungFrauen'). This painting of a mermaid was most probably done in the first decade of the 20th century, sometime between 1909 and 1910, when the houses here got renovated (repaired).
The painting shows a typical mermaid, a young naked woman with a fishtail. There are mountains in the background. This is a hint, that this mermaid isn't just an abstract mermaid, but is supposed to be a 'being' (spirit or ghost) that is existential in this particular lake (Hallstatt-Lake).
Looking a bit at the history of mermaids makes it clear: No new thing. Since the antique times in Egypt, Greece etc. there have been reflections in the arts and tales about mermaids.
Mermaids are more or less mythological beings, water spirits,nature spirits that try to insert an influence on people (mostly men).
One thing that is untypical in the picture above is that the mermaid got red hair. Usually mermaids are supposed to have green hair. As this painting is over a hundred years old and probably got darker in this last century, I virtually refreshed it with the photo - editing program paint.net.
In the indo-european mythology the element of the mermaids plays an important role in connection with the realm of death, the latter as being beyond a water, or under water. In the Edda a mermaid is a Lady over the souls of the drowning, a water spirit around the souls of the deceased.

The erotic component stands in apparent contrast to it, because in traditional societies everything is in a cycle of death and love and/or fertility and developing. These are endlessly repeating, each other causing principles.

Dance, singing and music are the joy of the mermaids, like the fairies (elfins). By singing, the mermaids actually pull listening younglings (teenagers) down into the depth. The mermaids are disastrous (or unfortunate) natures, limited natures, to the water as their element. Maybe they are a form of ancient celebrities.
In the Greek mythology a siren (Seirenes, Acheloides or Acheloiadesis) is a female fabulous creature (mixture nature of originally woman and bird, later also woman and fish), which attracts boat operators by its bewitching singing, in order to kill them (and get everlasting lifes 4 themselves).

In medieval times, the sirens were represented also as mixture natures of humans and fish and called sea virgins, depicted as beautiful women, whose bodies (not only their voices) are seductive.

In the moral myth interpretation of the ancient and medieval Christianity, sirens were considered as embodiment of the dangerous temptation outgoing from women. Considered as worldly attractions enticing to sense (wake up) desire.
In some more modern adaptions of the topic, sirens are equated with mermaids (sea virgins).
Concerning their all knowledgeness and death circumstances they resemble the sphinx (a 'se-mantic' creature knowing the past and the future).
A legend version told that the sirens itself entered (on the request of Hera) into a contest with the muses. The subject was: Who can sing more beautiful?

Someone (Kafka) said that "there's one thing that's more fatal than their song and that's their silence".