A former Olympic swimmer has captured astonishing footage of a “dolphin” swimming along the Thames in west London.
Andy Jameson was shocked to see the creature – thought be experts to actually be a porpoise - pop out of the waters in Richmond on Monday morning.
The commentator, who won bronze in the 100m butterfly at the 1988 Seoul Olympics, took a video of the animal as it surfaced for just a few seconds from the murky river.
Mr Jameson tweeted: “Ok .... you may all think I'm mad, but I just saw a Dolphin in the river Thames at Richmond.”
He later added: "Have to say I was very excited! Tiny little thing swimming very slowly .. but .. when the geese saw it they went nuts!"
A debate quickly broke out online over whether the animal was in fact a porpoise, or even a shark.
One person told him: “From the looks of the vid it's a Harbour Porpoise, rather than a dolphin, which is still very exciting.”
Mr Jameson said the rare sight made him feel “like David Attenborough” as he strolled along the riverside.
Stephen Marsh, operations manager for from voluntary group British Divers Marine Life Rescue, told the Standard it was definitely a porpoise rather than a dolphin.
He said: “It’s a porpoise. The dorsal fin of a dolphin would be far sharper."
Mr Marsh said it was likely to be one of two porpoises recently reported by the Environment Agency in a stretch of the river between Eel Pie Island and Teddington.
He said: “They’re fairly regular visitors to the Thames because the river is much cleaner now and there’s so much food for them.
“It’s a little bit high in the river but there’s no cause for alarm at all. It appears to be feeding.”
A 2015 survey by the Zoological Society of London found 49 whales, along with 450 porpoises and dolphins were seen in the Thames over a 10-year period.
The most famous visitor to the river was a juvenile northern bottlenose whale, dubbed the ‘Thames Whale’, which became stranded near the Albert Bridge in 2006.