Swan upping is an annual ceremony in England in which mute swans on the River Thames are rounded up, caught, ringed, and then released.

Why is it called swan upping?

The name of the ceremony is thought to originate from the call, "All Up" - a signal for the boats to circle a brood. Private owners of swans developed a complex system of markings, etched into the swans' beaks to identify them as private, and not Crown, property.

What does it mean to swan it up?

the taking up of young swans to mark them with nicks on the beak for identification. ... an annual expedition for this purpose on the Thames.