Ondine is the story of a water sprite, a mermaid of sorts, who falls for a mortal and he for her. Frederick Ashton choreographed it for Margot Fonteyn in 1958 and it worked because of her exceptional qualities as a dancer, and, perhaps, because those were more innocent times. You can’t imagine anyone making a ballet about sea nymphs today, especially one with such literal references to the briny, including green lipstick, iridescent unitards and women wafting aqua‑coloured chiffon and seaweed fronds to evoke storm-tossed waves.

Since its premiere 50 years ago, Ondine has been little seen, compared with, say, Kenneth MacMillan’s Manon and Romeo and Juliet, which between them and Mayerling are performed every season. You half think the Opera House big-wigs doubt Ondine’s appeal for audiences, yet within minutes of the curtain you are captivated.

Part of the reason is its very restraint and innocence. Anyone who has sat through crash-and-smash ballets will appreciate this. However, the main reason is simply because Hans Werner Henze’s music and Ashton’s choreography are so good.

The opening solo for Ondine herself (Tamara Rojo on opening night) is filigree mystery. The water sprite discovers her shadow, and then the nobleman Palemon (Edward Watson), and her delight in the mortal realm is palpable. The Divertissement dances in Act III beguile with their ingenuity and flair, while the hunting dances in the opening scene show Ashton at his slinkiest.

Another scene you don’t expect to work but does is in the boat sequence in Act II when the dancers sway in unison to suggest the briny. Their unified motion is so convincing, you hold on to your seat to steady yourself. Henze’s music is especially potent at this point.

That’s not to say everything about Saturday’s opener was perfect. Casting Genesia Rosato as Palemon’s earth-bound intended is not convincing. She is an able dancer but old enough to be his mother, making you doubt his attraction to her and his subsequent attachment to Ondine.
In addition, some of the corps lack aquatic commitment and seem strangers to Ashton’s style.

In rep until 6 December (020 7304 4000, www.roh.org.uk).