(Reuters) - A census of the Queen's swans has taken place annually on the River Thames for the last 800 years.
On Monday, a group of Boats led by the Queen's Swan Marker continued the tradition, known as "Swan Upping."
"We go up the river in six traditional rowing skiffs - every family of swans we come across, we will take them out of the water, we will take them a shore. We will weigh them, measure them and check them for any injuries," The Queen's royal Swan Marker, David Barber told Reuters.
Cygnets are individually tagged, as part of conservation efforts to protect the young birds.
"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," Barber added.
Dressed in their traditional livery, the teams use six traditional Thames rowing skiffs, each flying their flags and pennants.
It takes them five days to cover the stretch of the Thames between Sunbury near London out to Abingdon near Oxford.
They count all the adult swans and tag and monitor the health of cygnets by weighing them and checking in their mouths.
The river can be a dangerous place for the young swans, at risk from fishing hooks and wire.
A serious decline in the swan population in the mid-1980s was reversed when lead fishing weights were replaced with a non-toxic substance.
But growing demand for recreational use of the river has meant the river is still 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 said.
The tradition began in the Twelfth century where swans were often killed for food at banquets.
Barber said 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.