Here is a translation of Ovid's story of Salmacis. All its flaws are mine
As I said before, the story of Salmacis is a bit risqué, so I put it behind a spoiler warning.
Now learn ye why Salmacis is so infamous, why she emasculated men with her strong waves and softens all limbs they touch. Though the reason is obscured, the effect of this fountain is well-known.
Naiads raised the son that the Cytherean goddess [Aphrodite] had born to Mercury [Hermes] at the foot of Mount Ida. In his face you could recognize the father, recognize the mother; he carried the names of both of them [Herm-Aphroditus]. When he had lived there for fifteen years he left the hills and the Ida mountains that nourished him; he enjoyed discovering unknown landscapes and seeing new rivers, and his eager curiosity made the labours easy. He also came to the towns of Lycia and to the Carians who are neighbors to the Lycians. There he discovered lake with water so clear that he could see down to the deepest bottom. There are no muddy reeds, no bulrushes, no canes with pointed ends; crystalline and clear is the water, but the banks of the lake are green with lush grass and sweet-smelling herbs. A nymph lives here, but she does not like to hunt. She does not draw the bow or run through the forest with long steps; she is the only naiad unknown to light-footed Diana [the goddess of the hunt]. Rumour has it that her sisters often told her: “Salmacis, take the spear or the colourful quiver and exchange your leisure for an exciting hunt!” But she takes neither the spear nor the colourful quiver and does not exchange her leisure for an exciting hunt, but bathes her shapely limbs in the lake, frequently combs her hair with a comb made of boxtree and asks the waves that watch her how she could do her hair most attractively. Oftentimes she lounges on soft leaves or gentle herbs or plucks flowers; to do that she wraps herself in a shimmering translucent cloak.
And she was plucking flowers at the time she saw the boy and desired to have what she saw. Though she was in a hurry to approach him she did not walk towards him before she has primped her hair, checked her cloak, put on a smiling face and deserved to be called beautiful. Then she began to speak: “O boy who deserves to be called a god, if you are a god you could be Cupid. If you are mortal, then happy thy parents, happy your brother and truly happy your sister if you have one, and happy your wet nurse who fed you, but far more happy than those your wife if you have one, if you found one worth the marriage rites. If you are married, let my lust be secret, if not I want to be your wife – so let us lie down on the wedding bed.” Having said this the naiad fell silent. She noticed how he blushed (for he did not know yet what love was), but his blush became him. It was the red of the apple that hangs on a sun-soaked tree or the red of painted ivory or the colour of the moon when it turns red in the heat when the cymbals try to help her in vain [i.e. during a lunar eclipse which the Romans tried to prevent by making lots of noise].
The nymph keeps kissing him (not in a sisterly way) and is lifting her hands to his white neck when he says: “Stop it! Or I shall flee and leave all this and you!” Salmacis gets frightened, so she says “I shall leave this space for you, dear guest” and pretends to turn away and leave. But she looks back, hides in the bushes of the new forest and squats with her knees bent. Hermaphroditus walks here and there as if he were alone and not observed from the bushes, and when his feet touches the inviting waves of the lake, he enjoys the gently lapping waves and drops his clothes. Salmacis delights in this view and begins to burn in desire for his naked body. Her eyes glow and shine just like the most shining Phoebus [i.e. the sun] is reflected as a pure ball in the mirror. Hardly can she wait, hardly can she delay her pleasure, she wants to hold him in her arms and is close to losing her mind.
He has clapped his hands on his stomach in the meantime and jumps into the water. He swims through the lake hand over hand and his body shimmers in the water as if somebody has coloured ivory or a white lily in a light blue colour. “Victory! He is mine!” cheers the naiad, tears away her clothes, throws herself into the waves, lunges for the reluctant man, steals kisses from his mouth, lowers her hand, touches his unwilling chest and wraps herself around his body in various places. He resists her and tries to escape but she wraps herself around his body like snake wraps herself around the eagle that has captured it and tries to fly away with it (the head near the legs while the rear clings to the wings), or like ivy that wraps itself around the tallest trees or like the octopus that drown his enemy by wrapping all its arms around it. The Atlantiad [Hermaphroditus, grandson of Atlas] keeps resisting her and denies the nymph all the pleasures she had hoped to have from him; she presses him down and hangs on him with her whole body. “You may fight, insolent boy“, she says, „but you will not escape. Ye gods, this be your decree: No single day shall separate him from me nor me from him.”
The gods fulfilled his request: They joined both bodies and set one face on top of it. When two branches touch with their bark you will occasionally see that the grow on as one. Like that, these two are not two anymore where their bodies touched, but they have become one with a double form. It cannot be called woman and it cannot be called man, and it seems to be neither anymore.
As soon as he saw that the waters he had entered a man had emasculated him and softened his body, he raised his hands and said in a voice that was not a man’s anymore. “O father, o mother, grant you son who carries both your names, this one wish: Any man who steps into this lake shall leave it half a man and be effeminate by the waters he touched.” Moved by his request the parents fulfilles the wish of their double-shaped child and caused the fountain to be effeminating.