Now it dates back to the 12th century, but the poor weather has meant this year's Swan Upping ceremony on the River Thames has been cancelled for the first time in 900 years.
It's been a tough year for the local swan population. A virus meant the loss of many of the birds last year. And it's feared this summer's flooding means nests have been washed away.
The annual census - was due to start at Sunbury Lock in Surrey on Monday. Continuing through Berkshire, Buckinghamshire and Oxfordshire this week. Finishing at Abingdon Bridge on Friday.
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