The beluga whale spotted in the Thames for a second day in a row is “swimming strongly and feeding normally”, the RSPCA has said.
The animal welfare charity, which is monitoring the unusual arrival of the marine mammal, said there were no major concerns for its welfare.
The whale was first seen near Gravesend, Kent, on Tuesday, and has been spotted in the same area again on Wednesday.
Rescue teams have been on standby in case the animal, which is normally found thousands of miles away in the Arctic, gets into danger, and have urged people to keep their distance.
Conservationists said they hoped its instincts would soon kick in, and it would head out of the estuary and back north.
Beluga whales can grow up to 20ft in length and are usually at home in the icy waters around Greenland, Svalbard or the Barents Sea.
In a statement, the RSPCA said: “The whale is still in the Thames estuary, in roughly the same area off Gravesend as yesterday.
“At the moment, there are no major concerns for the welfare of the animal, as it seems to be swimming strongly and feeding normally, able to move fast in the water and dive.
“We want to ensure it is given the best chance of survival – and that means returning to the sea under its own steam.
“Following our request to the London Coastguard, we are pleased that local boats have moved away. Whales have acute hearing and become stressed very easily. ”
The whale was first spotted on Tuesday by ecologist Dave Andrews, who tweeted footage of the white animal.
“Can’t believe I’m writing this, no joke – BELUGA in the Thames off Coalhouse Fort,” he said.
The last reported sighting of beluga in UK waters was in 2015, when two were spotted off the Northumberland coast and one in Northern Ireland.
Among the theories of how the whale ended up in the Thames is that it followed a shoal of fish into the waterway.
Schooling fish such as herring, capelin and cod are among the usual sources of food for the species.
Rod Downie, polar chief adviser at WWF, said: “Beluga whales are a species of the icy Arctic – finding one in the tepid Thames is an astonishingly rare event.”
He said he hoped the whale would find its way home safely, but warned the species also faces threats in its Arctic home, including shipping, oil and gas development and loss of sea ice habitat due to climate change.
In 2006, a whale died after it swam up the river into central London despite rescue efforts.