On the shore of a lake in a forest meadow, Rusalka, a water nymph, sits, longing to be free from the world of spirits. Though human beings are merely mortal, she would like to become one of them, because she has fallen in love with a young man who comes to bathe in the lake. Her father, the Water Gnome, or Vodník, climbs out of the lake, warning her of the fatal consequences of such an infatuation, then returns to his element, leaving her in the domain of Ježibaba, a forest witch. Looking at the silver moon, Rusalka asks it to summon her lover. Ježibaba emerges from her hut and, with a spell, enables Rusalka to walk on land, agreeing to make the nymph human. But if she loses her mortal love, she must return to the water, and her lover will be doomed. Rusalka also must remain mute until her love is consummated. Retreating to her hut, Ježibaba brews a potion as a group of hunters approaches. One of them, the Prince, tells how he sighted a lovely apparition on this spot, only to have her recede into the water. Deprived of speech but given human form, Rusalka comes toward him as he sits by the lake. Fascinated, he embraces her.
At dusk a week later, in a park near the Prince's castle, a Gamekeeper and his nephew, the Kitchen Boy, comment on the excitement of the forthcoming wedding. They fear the Prince's strange sweetheart may be a water sprite, sent to lure him to his doom. They leave as the Prince approaches with Rusalka. A Foreign Princess, who hopes to marry the Prince herself, finds them and persuades him to lead her back to the ballroom, leaving Rusalka to ready herself for the ball. Dejected, the girl wanders off as her father climbs out of a nearby pond to watch the festivities through a window, fearing the worst for her. Seeing the Prince's head turned by the Princess, Rusalka runs from the hall, regretting having left her element: her lover has betrayed her, and now she is an outcast from both the mortal and spirit worlds. She meets her father, with whom she hides as the Prince and Princess come outdoors. Warmed by the Princess's mortal passion, the Prince succumbs to her. Running up to him, Rusalka throws herself into his arms, but he - now frightened of her - pushes her away. The Water Gnome, crying that the Prince will never escape Rusalka's love, draws her into the water. The Princess coldly tells the Prince to follow his other love into damnation, then leaves him.
At sunset, Rusalka sits by the edge of the lake, wishing she could die. When Ježibaba finds her, Rusalka tells how she was betrayed. To rejoin the spirit world, the witch says, Rusalka herself must kill her betrayer. Offered a knife, Rusalka in horror admits she still loves the Prince. As the witch leaves her, Rusalka slips back into the water, where her sister spirits shun her because of her contamination by mortals. As night nears, the Gamekeeper and his nephew approach the witch's hut with a message: the Princess has abandoned the Prince, who is now pining for the water nymph. Rusalka's father, rising from the lake, curses humankind for its treachery and frightens the two men away. The Prince enters in a daze, calling for Rusalka, who appears above the water, calling back to him. He asks to join her, whether in death or in life; she replies she is neither dead nor alive but doomed to wander like a ghost, adding that it is now her destiny to bring him to his death. Saying he cannot live without her, he throws himself into her embrace and dies.
Synopsis courtesy of Opera News.