Monday night was no ordinary night in London. If you were anywhere near Hammersmith Bridge on the River Thames, you would have seen the commotion as passersby crowded to watch the fin of what appeared to be a shark moving through the water.
The animal hasn't been seen since, leaving experts to pick apart the evidence.
So, was it a shark?
"It's highly unlikely", says Jack William, Senior Aquarist at Sea Life London Aquarium. "That far up the Thames the water is extremely fresh. It doesn't start getting salty until about Chelsea."
Fresh water is deadly to most species of shark, though there are a few that can survive in brackish waters, as well as one or two freshwater specialists.
The Port of London Authority agree, adding that it's "unlikely that any sharks would swim that far upstream."
"A shark? Shut up!" said one member of the public when asked by BBC London what they thought of the sighting.
More than 30 species of shark have been recorded off the British coastline, and some of these species have been spotted in the River Thames before.
"Sharks are a key part of the natural biodiversity [of the Thames]," says the Zoological Society of London. "The Thames Estuary is known to be home to at least five different species of shark, including the Critically Endangered tope shark and starry smoothhound sharks."
The tope shark, also known as the snapper shark, is a slender and elegant shark species, which can grow up to 6-feet long. It is often found close to the shoreline all around the UK. But don't fear, the species is harmless to humans – there has never been any record of an unprovoked tope shark attack.
"We do have several species of shark in UK waters, and you can find them around the estuary area," adds Williams, emphasising that it's the specific location within the River Thames system (freshwater) that makes it unlikely the animal sighted on Monday was a shark.
What else could it have been?
Other large marine animals have been seen in the Thames before, including a minke whale in 2021 and a pod a dolphins earlier this year. The Port of London Authority says the river has an "abundance of aquatic life with occasional visits from dolphins, porpoises and even whales."
It looks like the jury is still out.
Main image: fin of a shark – not the animal seen in the River Thames on Monday. Credit: Getty
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