The unusual sighting happened in the Gravesend area about 30 miles east of London.
The marine mammal has a distinctively round, melon-shaped head and beluga whales can dive up to 2,300ft (700m) blow the surface.
For anyone twitching the #BELUGA its been feeding around the barges (see last tweet for location) for the last hour and hasn't moved more than 200m in either direction. Still present. Heres another video @RareBirdAlertUK pic.twitter.com/S2qxKJyuuD
— Dave Andrews (@iPterodroma) September 25, 2018
“Beluga whales inhabit cold, arctic waters off Greenland, Svalbard and in the Barents Sea,” the group said in a statement. “There have only been around 20 sightings of beluga whales off the U.K. coast previously, but these have occurred off Northumberland, Northern Ireland, and Scotland.”
The whale that was spotted Tuesday was “obviously very lost and quite possibly in trouble,” the Whale and Dolphin Conservation said.
“As amazing as a beluga whale in the River Thames is, it poses a potentially tragic fate for it. Worrying yet extraordinary!”
Tweet: “Apparently there’s a beluga whale swimming around in #Thames estuary, near Gravesend. I really hope it’s okay!”
“This is the most southerly sighting of a beluga we have ever seen around these shores,” Lucy Babey, head of science and conservation at the ORCA charity, was quoted as saying by The Mirror newspaper.
“Can’t believe I’m writing this, no joke – BELUGA in the Thames off Coalhouse Fort,” ecologist Dave Andrews.