A former Olympic swimmer visiting the London suburb of Richmond was left baffled when he spotted a mysterious finned creature swimming in the River Thames.
Andy James, who represented England in the 1988 summer games, managed to capture footage of the puzzling sight and shared it on his Twitter account where he speculated that the creature may have been a dolphin.
The swimmer's followers soon responded with other possibilities for the creature, including a porpoise, a whale, and even a shark.
According to a group that tracks marine animal reports at the River Thames, there have actually been seven dolphin sightings already in 2017, so James' theory is not entirely out of the question.
What do you think the mystery creature might have been? Let us know at the Coast to Coast AM Facebook page.
Source: The Sun