By prerogative right, the British Crown enjoys ownership of all unmarked mute swans in open water.

Its main practical purposes today are to conduct a census of swans and check their health.

Over five days, the Crown's, the Vintners' and the Dyers' respective 'swan uppers' row up the river in skiffs (in recent centuries from Sunbury to Abingdon).

[4] Swans belonging to the Crown are left unmarked, except for a lightweight ring linked to the database of the British Trust for Ornithology.

The title which has stood for centuries and reflects the monarchs prerogative of ownership of all unmarked mute swans in open water.