Revellers planning to take part in the traditional May Day celebration on Oxford's Magdalen Bridge are risking serious injury, say police.
It is tradition to jump from Magdalen Bridge on May Morning
Every year thousands of people gather on and around the bridge to hear choristers sing hymns at dawn from the tower at Magdalen College.
But it is the tradition of people jumping from the bridge which is concerning Thames Valley Police.
They say the river is so shallow any jumpers could be seriously hurt.
A police spokesman said the river contained submerged rubbish like bicycles and supermarket trolleys.
Jeremy Fairbank, consultant spine surgeon at the Nuffield Orthopaedic Centre, said: "I know of at least three people who have sustained spinal factures jumping of Magdalen Bridge on May Day in the last ten years.
"If you jump from 20ft (4.5m) you risk sustaining factures; commonly of the heels, pelvis and spine."