A short video shot on the River Thames near Old Windsor Lock in Berkshire has prompted a swirl of online speculation after the animal seen swimming in the river drew competing identifications from experts and members of the public.
The footage, taken by 21-year-old Ryan Linehan while walking with his parents, shows a dark, furred head surfacing and submerging as the animal moves across the water. Linehan told Pen News the sighting was "a bit of a shock" and that the family first heard a local lock keeper suggest it might be a seal. Linehan said he doubted that explanation because the spot is roughly 30 to 40 miles from the sea.
Linehan described the animal as "slightly furry" with "a flat nose," and roughly the size of a medium to large dog. His mother, Bernie, 63, said the lock keeper alerted them and the son captured what she called "the best shot we could get." The footage was posted to a naturalist group on Facebook and quickly generated thousands of views and a debate over the creature's species.
Commenters proposed a range of possibilities. Some said it was a seal; others argued for a beaver, an otter, a sea lion, a turtle or even an escaped capybara. A few users made light of the sighting by invoking the Loch Ness monster. Online estimates cited in comments noted that the Thames now supports a substantial seal presence, including hundreds of animals observed in recent years.
Professional opinion also varied. When the Linehans contacted a local wildlife trust, a representative told them the animal was an otter. Florin Feneru, identification and advisory officer with the Angela Marmont Centre at the Natural History Museum in London, said he could not identify the animal "with any confidence" from the footage because the tail was not visible, but that he leaned toward beaver.
"I wish I could see its tail; that would have clearly settled the debate," Feneru said, explaining that beavers typically show a flatter, somewhat convex upper cranium profile, while otters have a distinct concave dip at the base of the muzzle. He added that the visible head shape in the footage suggested beaver rather than otter, though the quality and angle limited certainty.
Beavers were once extinct across Britain and have been reintroduced to selected rivers and waterways in recent decades, including parts of the Thames and some London waterways where they had not been present for about 400 years. Seals, too, have become increasingly visible in the Thames estuary and upriver stretches as populations recover and human-wildlife interactions rise.
The mix of possible explanations highlights both the challenges of identifying animals from brief, distant footage and the changing composition of wildlife in and around the Thames. Without clearer imagery showing the animal's tail, body shape and movement, experts said a definitive identification is unlikely.
Linehan said he and his parents do not plan further attempts to approach the animal and have left the matter to local wildlife groups. The footage remains online and continues to prompt comments and theories as specialists and amateurs weigh the evidence.
