The annual medieval tradition of counting the number of swans on the River Thames is under way.
The ancient ceremony dates back to when swans were a banquet delicacy
The Swan Upping tradition involves rowing skiffs from Sunbury, through Berkshire to Abingdon in Oxfordshire.
The swans and cygnets are weighed and ringed and each animal is checked for signs of injury and disease.
The ceremony dates from the 12th Century when the Crown claimed all unowned mute swans in Britain to ensure a ready supply for banquets and feasts.
Nowadays, the Queen retains the right to ownership on some stretches of the River Thames and tributaries.
Every year in the third week of July, The Queen's Swan Marker, David Barber, is joined by swan uppers from the Vinters' and Dyers' Livery companies, which were granted swan ownership rights in the 15th century, as he travels up the river.
Dressed in scarlet uniforms, the group travels in traditional Thames rowing skiffs, flying flags and rounding up broods of swans.
Every year, a number of swans are attacked by dogs, shot or hurt by fishing and swan upping can assess how prevalent these problems are.
Mr Barber said: "The focus of the pageant of Swan Upping has evolved over recent years to include the conservation of mute swans and their habitat.
"An essential part of this work involves the participation of children from local schools who are invited to join the Swan Uppers at different locations during the week."
The ceremony started at Sunbury-on-Thames on Monday and ends at Abingdon, Oxfordshire on Friday.