A family out for a stroll at Old Windsor Lock in Berkshire filmed a mystery animal swimming in the River Thames, footage that has since been viewed tens of thousands of times and prompted debate among naturalists and river authorities.
The clip, shot by 21-year-old Ryan Linehan while walking with his parents, shows a black head bobbing in and out of the water. His mother, Bernie Linehan, 63, said the creature looked "slightly furry" with a "quite a flat nose" and that its size appeared comparable to a medium to large dog, such as a German Shepherd.
The family first spoke to a local wildlife trust after the sighting. A trust representative told them she and colleagues thought the animal was an otter and said a seal or beaver would be unlikely to travel that far upriver or to be able to negotiate locks. The footage was then shared to a naturalist group on Facebook, where users suggested a range of possibilities, including a seal, beaver, capybara, coypu and even a sea lion, with commenters calling the clip everything from "Nessie, but she's a bit lost" to "110 percent a seal."
Experts contacted by reporters said the footage does not provide a definitive identification. Florin Feneru, identification and advisory officer at the Angela Marmont Centre, Natural History Museum, said he could not tell "with any confidence" and wished he could see the animal’s tail. "I can't see this as a seal at all," Feneru said, adding that he leaned toward beaver over otter because of the animal's upper cranial line, which he described as flatter and slightly convex.
Richard Bennett of the Canal and River Trust said he also could not be 100 percent sure but that the animal did not look like a seal and appeared "more beaver than otter from the shape of the head — something about the way it moves too."
The disagreement underscores the difficulty of identifying animals from short, distant video. Otters, beavers and seals can all be present in or near British waterways under the right circumstances. Beavers are native to parts of the northern hemisphere and are known for building dams and lodges using felled trees, sticks and mud to create still-water habitats. They are strong swimmers and build reservoirs that help them evade predators and overwinter. The largest beaver dam identified, at the southern edge of Wood Buffalo National Park in northern Alberta, Canada, measured 2,790 feet (850 meters) and was large enough to be seen from space.
Beavers have been the subject of reintroduction and conservation efforts in parts of the United Kingdom, but the presence of a beaver or other nonnative mammal upriver at Old Windsor would be notable and would likely prompt follow-up by wildlife authorities. Local trust staff in this case expressed skepticism that a seal or beaver would travel that far upriver and negotiate locks, while the museum and canal trust experts said the available image better fits a beaver than a seal.
At present, the identity of the animal filmed in the Thames remains unresolved. Observers and specialists say clearer footage showing the tail, body shape or distinctive movement patterns, or further confirmed sightings, would be needed to settle the debate.