Seals, dolphins and whales spotted in London
20 August 2015 Last updated at 07:42 BST
Almost three thousand seals, porpoises, dolphins and whales have been spotted in the River Thames, in London, in the past ten years, according to the Zoological Society of London.
The results of their latest Marine Mammal Sightings Survey has found that Canary Wharf, which has lots of tall buildings and people, is London's seal watching hotspot.
Their presence is a good sign that the Thames, which used to be polluted, is getting cleaner and supporting many fish species.
It also shows that urban environments, where there are lots of people and buildings, are still important for wildlife.