Melusina & I are rather like-minded.
Wikipedia describes the bathing mermaid thus:
Melusine (or Melusina) is a figure of European legends and folklore, a feminine spirit of fresh waters in sacred springs and rivers.
She is usually depicted as a woman who is a serpent or fish from the waist down (much like a mermaid). She is also sometimes illustrated with wings, two tails or both, and sometimes referred to as a nixie.
Melusine is sometimes used as a heraldic figure, typically in German Coats of arms, where she supports one scaly tail in each arm. She may appear crowned. The Coat of Arms of Warsaw features a siren (identified in Polish as a syrenka) very much like a depiction of Melusine, brandishing a sword and shield. She is the water-spirit from the Vistula who identified the proper site for the city to Boreslaus of Masovia in the late 13th century.
In "Minstrelsy of the Scottish Border: Introduction to the Tale of Tamlane on the Fairies of Popular Superstition" by Sir Walter Scott, Melusina's story is given briefly:
The fairy Melusina, also, who married Guy de Lusignan, Count of Poictou, under condition that he should never attempt to intrude upon her privacy, was of this latter class. She bore the count many children, and erected for him a magnificent castle by her magical art. Their harmony was uninterrupted until the prying husband broke the conditions of their union, by concealing himself to behold his wife make use of her enchanted bath. Hardly had Melusina discovered the indiscreet intruder, than, transforming herself into a dragon, she departed with a loud yell of lamentation, and was never again visible to mortal eyes ; although, even in the days of Brantome, she was supposed to be the protectress of her descendants, and was heard wailing as she sailed upon the blast round the turrets of the castle of Lusignan the night before it was demolished.
"Melusine" by Jean D'Arras is a longer version of her story, that I have yet to read.
To encounter the mermaid Melusina, as I first did, pick up a copy of "A Mermaid's Tale" by Amanda Adams. She knows her mermaids & the blue depths they haunt.
Julius Hubner, Melusine