In 1957 the River Thames was so heavily polluted it was declared “biologically dead” by the Natural History Museum leaving hope for marine life lost.

But now, more than 60 years after the museum's dismal proclamation, experts have counted over 100 seal pups on the river’s shores.

Scientists from the Zoological Society of London (ZSL), an international conservation charity, were "thrilled" to discover 138 pups on the sandbanks and creeks of the river in what is the first ever comprehensive count of the offspring.

Using a light aircraft, they were able to capture images during pupping season of the harbour seals, also known as the common seal.

The count is evidence that the London river’s ecosystem has come back from the brink after the National History Museum said its low oxygen levels and polluted waters would mean nothing could survive in its murky tides.

The pioneering research took place in 2018, with the data released for the first time today. It saw scientists carefully analyse hundreds of photos taken as part of UK-wide seal monitoring initiative.

Explaining the decision to count using photographs, ZSL said it was “much easier, and so more accurate, to count the seals in photos instead of the constantly moving, playful creatures”.