A village once stood outside the Old Town walls, and a pond there was home to a sad but beautiful mermaid
The Czech word for a little pond is Rybníček, and in pagan times a village by that name stood outside the Old Town walls in what is now Prague’s New Town section. It is still remembered by two streets called Na Rybníčku (On the Little Pond) and V Tůních (In the Pools). The group of three small ponds is long gone now, but one used to be home to a mermaid.
A widow, from a long line of pagan seers and healers, lived in the village with her teenage daughter. The widow married a ferryman who worked on the Vltava river. This was long before Charles Bridge (or the earlier Judith Bridge) was built, so the ferryman made a good living.
But the widow soon found out it was not her, but her daughter the ferryman was interested in. One night when the ferryman was trying to force his unwanted affections on the seriously uninterested daughter, the widow pounced on them both.
She threw the ferrymen out on his ear, and cursed him and her innocent daughter to forever live in the water where they belonged. The ferryman turned into a water sprite (vodník) and wandered off to join the other dripping little green men, never to be heard from again.

The daughter became a mermaid and slipped into the pond at the intersection of what is now Na Rybníčku and V Tůních.
For decades, long after the locals forgot about the widow and the ferryman, she would climb onto a rock by the edge of the lake on moonlit nights and sing her sad song while she braided tall grass and wild flowers into necklaces, bracelets, belts and headbands to accent her never-fading beauty.
After her experiences as a teen human girl, she had grown wary of humans and tried to avoid them. Whenever someone approached, she would slip back into the water and stay there. The pond wasn’t very deep, but any attempt to find the mermaid in the daytime was fruitless.
A teenage boy fell in love with the mermaid, and would watch her, night after night, as she dressed herself in flowers and looked at her reflection. One night he crept up to her and managed to grab her before she could jump into the pond.

She struggled and tried to tell the boy off, saying that life together would be impossible. But he wouldn’t listen. The boy confessed his deep love, talking nonstop till almost dawn, and the mermaid eventually started to like him back because of his naive and simple ways.
Finally she told him that there was a loophole, or at least other mermaids had mentioned one. If the boy’s mother agreed to hold a proper formal wedding, she could revert back into being a fully human girl. But the mother must agee to this of her free will, without any coaxing ahead of time.
The next night the boy brought his unsuspecting mother to the pond to meet his beloved. The mother, though, was not impressed. She said no supernatural being would ever have her son.
Insulted and humiliated again, the mermaid jumped into the pond and swam below the surface. Desperately in love, the boy jumped in after her and neither was ever seen again.
The boy’s mother resented her rashness, but nothing she tried ever brought the boy back.
Background
Prague’s New Town isn’t very new. It was planned by Emperor Charles IV in 1348, based on stylized maps of Jerusalem. Charles had the idea that if he built a new holy city, God would come there on Judgment Day, instead of going to the original Jerusalem, which at that time was not under Christian control.
The village called Rybníček, meaning Little Pond, already existed in 993, when it is first mentioned. In the 12th century, the village’s round church called the Rotunda of St Stephen, was built. Today it is called the Rotunda of St Longin, but is seldom open and was almost torn down in the 19th century, but preservationists intervened.

It has long been displaced by the large Church of St Stephen across the street, on the corner of Na Rybníčku and Štěpánská streets. The churchyard once housed a cemetery for executed thieves and deceased foreigners. That yard is now a school playground.
The mermaid tale is unique in Prague, but water sprites are quite common, featuring in fairytales and legends, such as Kabourek, who was famous for drinking beer at pubs on Kampa island.
A stone house sign, which used to be used to identify houses before they were numbered, featuring a mermaid can be found at Karlova 14 in Old Town. The house is called House at the Stone Mermaid (Dům U Kamenné mořské panny). Mořská panna is literally “sea virgin.”

Another image of a mermaid can be seen on the fresco-decorated porch of the Wallenstein Palace, visible from the Wallenstein Garden. She is featured on the Page of Cups in The Tarot of Prague deck.
Slavic folklore also refers to a female human-fish creature as a Rusalka, though these are more a type of water demon who can be quite harmful. Rusalkas are associated with the souls of young women who drowned or committed suicide.
In many tales across cultures, beautiful mermaids lure men into drowning themselves so the mermaid can steal the victim’s soul to replace her own soul that has been lost. A mermaid is depicted on the municipal coat of arms of Warsaw.
The image used by a popular coffee chain, by the way, is not a mermaid since mermaids have one tail. The twin-tailed sea creature is a melusine. The House of Luxembourg, of which Emperor Charles IV is a descendant, is said in legend to have sprung from a melusine.
A melusine also is sometimes depicted as having wings, so the Wallenstein mermaid could be a melusine instead.
Main image: Havfrue, by Elisabeth Jerichau Baumann, 1873, public domain.