A rare beluga whale reported to be swimming in the Thames near Gravesend could be "in trouble", conservationists have warned.

Ecologist Dave Andrews tweeted footage of the marine mammal, which he said was swimming in the river off Coalhouse Fort, Essex.

He said: "Can't believe I'm writing this, no joke - BELUGA in the Thames off Coalhouse Fort."

He added the beluga had been feeding around barges on the river for around an hour and had not moved more than 200m either direction on the river.

While the report of the animal prompted excitement on social media, conservationists warned that the beluga whale, normally found in the High Arctic, was lost and could be in trouble.

Danny Groves, from Whale and Dolphin Conservation (WDC) said: "This is a High Arctic species thousands of miles from where it should be in Greenland, Svalbard or the Barents Sea, they are usually associated close to the ice.

"He or she is obviously very lost and quite possibly in trouble. "

He urged people to give the whale "space and minimise disturbance".

They show a white, whale-shaped animal swimming in the sea.

The RSPCA has said it is investigating the incident.

The charity says it is "sending an officer" to look further into the matter as videos and reports circulate on social media.

The public is being urged not to try and get near the whale. 

News Shopper:

Beluga whales, pictured above, are usually found in Arctic and sub-Arctic waters.