Once declared biologically dead and smelling of rotten eggs, the Thames has bounced back and is teeming with marine life.

In 1957 many would have been surprised to hear life would flourish in the polluted waters again, but a study by the Zoological Society of London shows the waterways are full of mammals.

Between 2004 and 2014, 2,732 marine mammals were spotted.

Steve Bolam, Molesey Lock keeper, said: “We do get salmon, sea trout and the occasional seal coming up stream because it is cleaner.”

Seals are regularly spotted in the stretch of river from Richmond to East Molesey.

In January and February, a grey seal was also seen between Molesey Lock and Teddington Lock, while last month a harbour porpoise was seen in the water between Thames Ditton and Hampton Court Park.