Britons are rowing around the River Thames counting all of the swans owned by the Queen -- and it's produced some delightful photos

Swan upping skiffs thrashingScott Barbour/Getty ImagesThis swan doesn’t want to be caught.

It’s the third week of July, and that can only mean one thing: The annual British Swan Upping!

Today, the Swan Upping is conducted as part of a yearly census of swan populations on the River Thames in an effort to conserve their numbers and check up on their health.

But the traditional ceremony stretches more than 800 years, when swans were treated as a status symbol as well as a delicay.

The first thing you need to know about British swans: The Queen owns all of them. It's one of her many 'prerogative' powers, a hangover from when the monarchy was in a position of real power in Britain.

However, she only chooses to exercise this ownership on 'certain stretches of the Thames and its surrounding tributaries,' according to the Royal Family's official website.

The Queen is joined in her ownership of swans by the Ilchester family, as well as the Worshipful Company of Dyers, and the Worshipful Company of Vintners. They were 'granted the privilege of ownership' in the 15th century.

It is along this 79-mile stretch of the Thames that the Swan Upping takes place, over the course of a week.

Six skiffs row up the river during the Upping -- two belonging to the Crown, two to Vintners, and two to the Dyers.

Each skiff is decked out in the appropriate livery, with the uppers wearing traditional uniforms.

According to the Swan Upping promotional brochure, Royal ownership of swans dates back to at least 1186. 'It was desirable to own swans because the young birds, (cygnets), were highly valued for food and often served at banquets and feasts,' it explains. The Swan Upping was how these cygnets were rounded up.

Historically, swans were also marked to identify ownership by cutting marks into their bills. Today, swans caught in the Upping are simply ringed.

Swans aren't eaten in Britain today, either. The Swan Upping continues to exist solely as a conversation effort.

Note the ring on the swan's left leg.

Swans are weighed, measured, checked for illnesses, and counted.

One threat to swans is air gun shootings. Two breeding pairs were killed in shootings this year, which is punishable by a six-month jail sentence.

But a more widespread threat to swans on the River Thames is getting ensnared in fishing tackle. Poisonous lead tackle was especially dangerous before it was banned in the late 1980s. Numbers have recovered since 1985, when there were just seven breeding pairs left on the London-Henley stretch of the river.

When a brood of cygnets is sighted, the uppers shout 'All-up!' before surrounding the birds and capturing them.

The swans are safely released afterwards.

Nonetheless, not all swans are too happy to be caught!

The general public is welcome to watch the Upping, and a number of viewing points are set up along the river each year.

The efforts are led by the Queen's Swan Marker. David Barber, pictured, has held the position since 1993.

The Queen also has a Warden of the Swans -- a position currently held by Professor Christopher Perrins (bottom left). Perrins is a Emeritus Fellow at the University of Oxford.

Sometimes the Queen attends herself (although she travels in a bit more luxury and style than the uppers).

According to the Royal Family's website, 'on passing Windsor Castle, the rowers stand to attention in their boat with oars raised and salute 'Her Majesty The Queen, Seigneur of the Swans'.'

In its 800-year-old history, the ceremony has only been cancelled once, according to the BBC -- in 2012. Heavy flooding disrupted the event, with Barber explaining that 'boats aren't allowed on (the Thames) at this time nad it would simply not be safe to carry out the census. There's simply nothing we can do about it.'

Last year, the swan upping counted 2,014 swans, including 34 breeding pairs and 120 cygnets, the BBC reports.

This year's census won't finish until Friday, but Barber sounds positive. 'Our expectations are that numbers should be better than last year,' he says.

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