Tchaikovsky gave the world Swan Lake, from Yeats came Leda and the Swan. Now comes Germany's contribution to aquatic fowl legend: the swan and the pedal boat. Petra is a rare Australian black swan, her pedal-boat lover is plastic, shaped like a common white swan. Yet, as in all proper romances, love is blind.

To curious observers, it is clear Petra has lost her heart to the vessel which is up for hire on a boating pond in northern Germany. Despite efforts of municipal workers at the lake to separate her from her plastic partner, the love affair goes on and the staff have had to accept the unusual bond.

It was last year that the link was formed. As news of the strange relationship spread, tourists flocked to witness Petra's passion for the boat. She was seen circling her plastic companion, staring endlessly at it and making crooning noises - behaviour observing naturalists said showed all the typical signs of a swan in love.

But as winter closed in Petra refused to fly to warmer climes and would not leave the object of her affections. Worried about her fate in the Muenster region, where temperatures regularly fall into the minus figures during the winter, park keepers met to discuss what they could do.

The boats are taken off the water in winter to protect their hulls. Owner Peter Overschmidt said: 'When you see how Petra circles the swan boat, you know there could be no other option. It's the centre of her life.'

The local Allwetter Zoo agreed that both the bird and the boat could spend the winter on its pond near the elephant enclosure, which is more protected from the elements than the lake. Zoo director Joerg Adler said: 'This arrangement could go on forever because the animal believes she has found a partner for life.'

A winter quarters for both boat and swan are now planned.