A glade at the edge of a lake
Deep within the forest, three nymphs playfully tease Vodnik as he tries to catch one of them. His daughter Rusalka tells of her sadness – she wishes to be mortal in order to pursue her love for a princely young man who swims in the lake. Vodnik tries to dissuade her, for he only sees doom in the world of humans, but she will not be deterred. She prays to the moon, hoping the Prince may return her affection.
Rusalka visits Ježibaba, an old sorceress who is willing to help. The witch has the necessary potion, but it has one side-effect – after her transformation, Rusalka will no longer be able to speak. If she should not find lasting love among humans, she will be forced to walk through life accursed. Rusalka bravely drinks the magic philter.
As dawn breaks, a hunting party is in pursuit of game. The unsuccessful predators retire, but the Prince remains behind, magically drawn to the lake. Meeting Rusalka for the first time, he immediately falls in love.
The castle grounds
A gamekeeper and turnspit prepare for the royal feast. They gossip about a speechless beauty the Prince found in the forest, whom they believe he will marry. The superstitious gamekeeper fears danger, as the woodland is full of spectral creatures.
Rusalka enters with the Prince, who is puzzled by her continued silence and her sad disposition. Still enthralled, he vows to better understand his future bride once they are wed. One of the party guests, an alluring foreign princess, reproaches the Prince for ignoring the festivities. The Princess lightly mocks Rusalka’s speechlessness, quietly enraging the former nymph, as she shamelessly escorts the Prince to the party inside. Vodnik consoles his pitiful daughter as she watches the Princess successfully entice the Prince with her beauty.
A glade at the edge of the lake
Tearfully, Rusalka has returned to the forest, ready to forsake humankind. Ježibaba agrees to switch Rusalka back to her original state, but as a result, her lover may never return, lest he die from her embrace. The witch even offers a knife so that she may kill the Prince and cleanse herself of his mortal touch, but Rusalka refuses and returns to the lake.
The gamekeeper and turnspit enter with trepidation, in search of a cure for their ailing prince who has fallen ill, presumably from Rusalka’s spell. Ježibaba eyes the fearful turnspit, whom she believes would make a tasty meal, but Vodnik scares them off. The nymphs again try to play, but he sadly admits that their carefree world has been marred by the stain of mankind.
The Prince feverishly searches the woods for his lost love, and in a dreamlike state, Rusalka hauntingly appears before him. She scorns his renewed affection and cautions that his fate will be sealed with just one caress. Ignoring her warning, the Prince kisses Rusalka, then dies in her arms.