Buckingham Palace has announced that the annual Swan Upping, a tradition dating back to the 12th century which involves a census of the swan population on the River Thames, will be conducted by the queen's official Swan Marker from July 20-24.

"With the assistance of the Queen's Swan Warden, Professor Christopher Perrins of the University of Oxford, the swans and young cygnets are also assessed for any signs of injury or disease," Buckingham Palace said in announcing the count.

The process involves the Swan Marker, David Barber, rowing up the Thames for five days with the Swan Warden in traditional skiffs while wearing special scarlet uniforms and counting, weighing and measuring swans and cygnets.

It may seem eccentric, but it is very important to the queen.

It is also an important year because Queen Elizabeth has decided to join her team of Swan Uppers for part of the census.