A beluga whale, stranded in the River Thames outside London since Tuesday morning, is probably the furthest south one of the creatures has been seen in the UK, ecologist Michael Hoit told Euronews.
The creature is thousands of miles from its normal Arctic habitat, which makes this an "extremely unusual sighting," said Hoit.
Belugas often feed in estuaries, so the Thames is not a bad habitat for the pure-white marine mammal, but it is "very much out of place".
As the medium-sized whale is looking "pretty healthy" Hoit was hopeful the animal could find its way back out to sea. "Keep your fingers crossed for him," the ecologist said.
Location of the whale
The rare sighting off Gravesend on Tuesday was shared by ecologist Dave Andrews who tweeted: “Can’t believe I’m writing this, no joke – BELUGA in the Thames off Coalhouse Fort.”
His video footage showed the white mammal surfacing.
In a further tweet today, he said the whale is still in the Thames.
Photos shared also showed it breaching near a buoy on the estuary yesterday.
Vessels were kept clear - and the British Divers Marine Life urged the public not to get too close.
Nature observer, Jacques Turner-Moss, also spotted the whale.
He tweeted: “The docks on the Thames by Gravesend aren't really the backdrop where you'd imagine seeing your first Beluga but today I saw just that...”
The ORCA conservation charity said the whale was far from its normal range and they were monitoring it carefully.
In a statement on its website, ORCA’s Head of Science & Conservation, Lucy Babey, said: "It's an incredibly unusual sighting, with the most recent record of belugas around the UK being in Northumberland in 2015.
“Considering how far the animal is from it's range, it may be distressed and so it is vital that onlookers both on land and at sea keep their distance."
The last sighting in UK waters was in 2015 when they were spotted off northeastern England near the Northumberland coastline, but they left shortly afterwards.