A census of the Queen's swans has taken place every year on the River Thames since the twelfth century. Known as "Swan Upping", the 800 year-old tradition sees six rowing boats travel through the waters, removing the swans from the water so that they can be weighed, measured and checked for injuries before they are returned to the river. The group of boats, led by the Queen's royal Swan Marker cover the stretch of the Thames on a five day journey from Sunbury to Abingdon.

Swan Upping
Swans and cygnets are rounded up to be weighed and tagged on the River Thames, South West LondonDan Kitwood/ Getty Images

As well as health checks, the royal birds are also individually tagged - this is of particular importance to the cygnets because it is seen as part of conservation efforts to protect the young birds. The river can be dangerous place for the younger swans, who are at particular risk from getting caught in fishing hooks and wire. "A lot of the injuries we get these days is through fishing tackle. When the cygnets are very young, they get caught in fishing tackle quite easily," The Queen's royal Swan Marker, David Barber, told Reuters.

Swan Upping
David Barber, The Queen's Swan Marker, prepares to set off for Swan Upping at Sunbury, Southern EnglandToby Melville/ Reuters
Swan Upping
Swans and cygnets are rounded up to be weighed and tagged on the River Thames, South West LondonDan Kitwood/ Getty Images
Swan Upping
A young cygnet is carried after being weighed by the River Thames, South West LondonDan Kitwood/ Getty Images

There was a serious decline in the swan population in the mid-1980s, which has been reversed after lead fishing weights were replaced with a non-toxic substance. However, the growing demand for recreational use of the river has meant its waters remain a dangerous habitat for the royal birds. "We've had a lot of problems over the last few years. Last year we had 83 cygnets that we caught, weighed and measured. The year before, we had 120, so you can see it has declined," Barber explained.

The tradition began at a time where swans were often killed for food for banquets. Barber explained that the royal involvement in the process can be traced back to then. "Her majesty has the right to own any swans swimming in open waters in the United Kingdom if she so pleases," he added. Those who carry out the tradition hope that it helps conserve the future of the birds and educates younger generations about their importance and welfare.

Swan Upping
Teams raise a toast at the end of the first day of the annual Swan Upping census on the River Thames, South West LondonDan Kitwood/ Getty Images
Swan Upping
A Mute Swan and cygnets make their way along the River Thames on the River Thames, South West LondonDan Kitwood/ Getty Images
Swan Upping
Swans and cygnets are rounded up to be weighed and tagged by the River Thames, South West LondonDan Kitwood/ Getty Images
Swan Upping
A swan is restrained whilst being examined near Shepperton, Southern EnglandToby Melville/ Reuters
Swan Upping
A member of the Dyers team fixes a broken rudder during the annual Swan Upping census on the River Thames, South West LondonDan Kitwood/ Getty Images
Swan Upping
Swans and cygnets are rounded up to be weighed and tagged on the River Thames, South West LondonDan Kitwood/ Getty Images
Swan Upping
Swans and cygnets are rounded up to be weighed and tagged by the River Thames, South West LondonDan Kitwood/ Getty Images
Swan Upping
A Swan flower pot on the front of a boat during the annual Swan Upping census on the River Thames, South West LondonDan Kitwood/ Getty Images
Swan Upping
Detail is seen on a crew members hat during the annual Swan Upping near Shepperton, Southern EnglandToby Melville/ Reuters
Swan Upping
A girl looks at a young cygnet after it is caught on the River Thames, South West LondonDan Kitwood/ Getty Images
Swan Upping
A cygnet is measured on the River Thames, South West LondonDan Kitwood/ Getty Images
Swan Upping
A cygnets feet are tied to stop it struggling before it is weighed on the River Thames, South West LondonDan Kitwood/ Getty Images
Swan Upping
David Barber, The Queen's Swan Marker holds a cygnet at Sunbury, Southern EnglandToby Melville/ Reuters