Wiktionary
n. An annual swan census in Britain in which mute swans on the River Thames are rounded up, caught, marked, and released.
Wikipedia
Swan Upping is an annual ceremonial and practical activity in Britain in which mute swans on the River Thames are rounded up, caught, marked, and then released.
Traditionally, the British Monarch retains the right to ownership of all unmarked mute swans in open water, but only exercises ownership on certain stretches of the River Thames and its surrounding tributaries. This tradition dates from c. the 12th century; It was formalised with a Royal Charter of Edward IV passed in 1482, establishing "How much land he must have which shall have a mark or game of swans", preventing the claim of ownership of swans by "yeomen and husbandmen, and other persons of little reputation".
Swan Upping is a means of establishing a swan census through a process of ringing the swan's feet and today also serves to check the health of swans. Swan Upping occurs annually during the third week of July. During the ceremony, the Queen's, Vintners' and the Dyers' Swan Uppers row up the river in skiffs. Swans caught by the Queen's Swan Uppers under the direction of the Swan Marker are unmarked, except for a ring linked to the database of the British Trust for Ornithology (BTO). Those caught by the Dyers' and Vintners are identified as theirs by means of a further ring on the other leg. Today, only swans with cygnets are caught and ringed. This gives a yearly snapshot as to how well Thames swans are breeding. Originally, rather than being ringed, the swans would be marked on the bill, a practice reflected in the pub name The Swan with Two Necks, a corruption of "The Swan with Two Nicks".
On 20 July 2009, Queen Elizabeth II, as "Seigneur of the Swans," attended the Swan Upping ceremony for the first time in her reign, and the first time that the monarch has personally watched the ceremony in centuries.
In 2012, because of flooding of the river from adverse weather, the ceremony was cancelled between Sunbury-on-Thames and Windsor, according to BBC News "for the first time in its 900-year history".
on the upper Thames - swan-upping (1875).jpg|"Swan Upping on the Thames", from Henry Robert Robertson's Life on the Upper Thames, (1875) upping at Henley.jpg|A Queen's swan upper with a mute swan during 2010 swan upping at Henley-on-Thames ' swan marker.jpg|Swan marker of the Worshipful Company of Vintners, in his blue uniform, during 2011 swan upping, Abingdon. Upping at Cookham.jpg|Swan Upping at Cookham, by Stanley Spencer, oil on canvas, 1915-19