NO OPPORTUNITY of hearing Dvorák’s operatic masterpiece is ever unwelcome, but in spite of the Royal Opera’s often excellent performance this is an odd exercise.

It would be even odder if the motivation for this week’s two “concert stagings” of Rusalka were less transparent. Concert slots at Covent Garden are normally reserved for obscure operas not quite deserving the full treatment, but here one of the most magnificent scores in the repertory is taking the place of a rarity that might well have been offered in anticipation of the Dvorák centenary. Why? Answer: the Fleming Factor. Rusalka is apparently one of the favourite roles of the American soprano Renée Fleming.Fleming is also box-office friendly, so to everyone this must seem the ideal end-of-season offering.

Everyone except the shade of Dvorák, that is. Fleming may be better suited to his music than some of the composers she sings, but she can fall wide of the stylistic mark. In the famous Song to the Moon she drags and croons alarmingly, and the conductor Charles Mackerras is surprisingly tolerant. Elsewhere, he shows again why he is surely the greatest interpreter of Czech music today, drawing an orchestral account by turns translucent and muscular.

Fleming produces glowing tone in her upper register, but often the voice sounds thin and insecure. She tries to compensate with choreography of the couture and, to make up for an absence of real emotion in the musical performance itself, mimes wild anguish. It doesn’t help her that two vocal masterclasses are taking place. Eva Urbanova blazes away as the Foreign Princess, and Larissa Diadkova brings magnificently focused tone to her imprecations as the witch Jezibaba.

Sergey Larin is a refined Prince, and Franz Hawlata solid if undercharacterised, more Water Board than Water Sprite. But Martina Bauerova is idiomatic as the Kitchen Boy and Sally Matthews, Ailish Tynan and Tove Dahlberg make a delightful trio of Nymphs.

Box office: 0207-304 4000