As infestations of the supernatural go, an invasion of the water sprites is better than most. We’ve been in the midst of one for months, starting with all the pieces about ancient Greek sea gods and semi-deities in the annual S.F. Olympians Festival and the Children’s Musical Theatre of San Jose’s production of Disney’s “The Little Mermaid.” Now comes Cutting Ball Theater’s “Ondine,” which opened Thursday, Feb. 11, and will be followed by “Selkie” at Z Space (opening Saturday, Feb. 13), both of which are world premieres.

We’ll leave the selkies for later. They’re sea creatures who can shed their sealskins to act as humans on land, usually with tragic results when they fall in love. Ondine is less a species than an individual water sprite who, in many varied tellings, falls in love with a man at considerable risk to her immortality and/or his life. the subject of countless European folk tales and literary works such as Jean Giraudoux’s drama “Ondine,” performed by We Players at Sutro Heights last summer.

Katharine Sherman’s “Ondine” for Cutting Ball, though no less densely poetic, is a very different type of drama — an extended tone poem on love, alchemy, breath, water and sleep deprivation. Luxuriantly staged by Rob Melrose, and performed with athletic grace and playfully sensual intensity by Jessica Waldman and Kenny Toll, it’s less a story than a reverie within the legend’s tragic climax, interrupted by flashbacks to moments in the romance up to this point — that gradually reveal its significance.

So, serious spoiler alert: If you don’t know what’s at stake, you may be befuddled by much of the action leading up to its revelation. But if you do know, you might be underwhelmed when it comes. Those planning to see this “Ondine” should read no further.

Waldman’s Ondine and Toll’s Hildebrand are already desperately attempting to stave off fate when we enter. They’re cuddling, toying with each other and running back and forth on Michael Locher’s metaphoric set, a great, dark curved platform rising to wave-like crests at each end. He’s exhausted, ready to fall asleep whenever he stops moving. She’s watching him intently, gently or insistently — often apologetically — prodding him to stay awake.

The reason (remember the spoiler alert) is the curse she’s laid on him, that if he falls asleep he’ll stop breathing — not, as in many versions, because he’s been unfaithful to a woman but because he’s left her home alone too long in pursuit of his passion for alchemy. Knowing that adds considerably to the complex beauty of Sherman’s lyrical interplay of alchemical, emotional and culinary interactions with the rhythms of breath and the sea.

But despite the sweet beauty of Ondine and Hildebrand’s first-love delight and her learning how to be human, the story essentially spins its wheels for a full 70 minutes. Even the brightly staged visits of her sea-nymph sisters (Molly Benson, Marilet Martinez and Danielle O’Hare) begin to seem repetitive. Besides, the danger of a theatrical reverie about fighting off sleep is that it may make you feel the same.