Ten years of public sightings show that large marine mammals are regularly found in England’s River Thames.
The Zoological Society of London (ZSL) has received records of 2,732 animals over that period.
Seals were the most common animal seen, with many spotted around London’s Canary Wharf, probably because many people spot them from its skyscrapers.
In addition, the public reported 444 porpoises and dolphins on the river, and 49 whales.
Joanna Barker, ZSL’s European conservation projects manager, said: “Many people looking into the Thames see a murky, dirty environment.”
“But, actually, beneath the waves, it is full of life. We have a huge range of fish and invertebrates, and also top predators.”
Just 50 years ago, the Thames was so polluted it was declared “biologically extinct“, too dirty for anything to survive there.