Large sharks are living in the Thames with the river now playing a "vital role" in preserving endangered species.
The Greater Thames Shark Project, run by the Zoological Society of London (ZSL), has identified Tope, starry smooth-hound and spurdog as shark species identified in the river.
The project, which started last year, is designed to gather more data on the three elusive types of shark residing in the Thames’s outer estuary.
According to a summary of the project, the tope shark is a critically endangered species globally, while the starry smoothhound has recently been downgraded from endangered to near threatened.
Tope sharks, which have distinctive long snouts, grow up to 6ft and have been known to be aggressive.
Spurdogs, which are also classified as endangered, swim in shoals and have two dorsal fins which release venom. This venom can cause extreme discomfort and swelling in humans.
Both species are believed to use the estuary to give birth to their young and nurse their pups. The project summary says this gives the Thames a “vital role” in the long-term survival of the species.
According to the Zoological Society of London (ZSL) the Thames is now teeming with life and supports over 115 species of fish and 92 species of bird in its almost 600 hectares of saltmarsh.
Critically endangered eels, seahorses, oysters and seals are also among those creatures found in the health check.
Tope, Starry Smoothhound and Spurdog sharks are using the river as a nursery as adults like pupping in shallow bays and estuaries.
Young sharks are remaining there for up to two years.
Critically endangered eels also seem to be making a comeback.
Alison Debney, of ZSL, said: "Estuaries are one of our neglected and threatened ecosystems.
"This report has enabled us to really look at how far the Thames has come on its journey to recovery since it was declared biologically dead, and in some cases, set baselines to build from in the future."
This first State of the Thames Report also shows how the river is helping protect vulnerable animals and identifies the threats it faces from climate change.
Since the early 1990s, the number of fish species in tidal areas has declined - and we're not sure why.
Moreover, the temperature of the capital's waterway has risen by 0.2C per year in recent times which, combined with sea level rises, is worrying for wildlife.
Yet, water quality has improved with dissolved oxygen (DO) concentrations showing a positive, long-term increase from 2007 to 2020.
Less than 45% DO can kill fish and impact relationships between key species that live in the river.
Overall, phosphorus concentrations have decreased since the 1990s thanks to improvements at sewage treatment works, but there has been a long-term increase in nitrate concentrations which can damage wildlife.
The Environment Agency has identified industrial and sewage waste as the main source of nitrate in London's waters.
In addition, there are many chemicals of concern that are not being regularly monitored which have potentially harmful impacts on wildlife.
Liz Wood-Griffiths, head of consents at Tideway, said: "This report comes at a critical time and highlights the urgent need for the Thames Tideway Tunnel, known as London's new super sewer.
"The new sewer, which is due to be complete in 2025, is designed to capture more than 95% of the sewage spills that enter the River from London's Victorian sewer system.
"It will have a significant impact on the water quality, making it a much healthier environment for wildlife to survive and flourish."
