- Ecologist Dave Andrews tweeted videos off whale off Coalhouse Fort in Essex
- He said whale had been feeding around barges near Gravesend for an hour
- But marine biologists were concerned about 'potentially tragic fate' for whale
A rare whale dubbed 'Benny the beluga' was spotted in the River Thames near London today, in what is believed to be the most southerly sighting ever recorded in Britain.
Ecologist and ornithologist Dave Andrews could not hide his surprise as he tweeted videos of the mammal in the Thames off Coalhouse Fort in Tilbury, Essex.
He said the whale was close to Gravesend in Kent, and added on Twitter: 'Can't believe I'm writing this, no joke - beluga in the Thames off Coalhouse Fort.
'For anyone twitching the beluga, it's been feeding around the barges for the last hour and hasn't moved more than 200 metres in either direction. Still present.'
He added that the whale - hundreds of miles from its normal Arctic habitat - was 'best viewed from Kent just off Shorne marshes but don't know access to this area'.
Aspiring marine biologist Beth Clyne, 20, of East Yorkshire, tweeted: 'I'm freaking out about this beluga in the River Thames! I'm that shocked, I don't know what to think.
'As amazing as a beluga whale in the River Thames is, it poses a potentially tragic fate for it. Worrying yet extraordinary!'
A grab from one of the videos of the whale in the Thames off Coalhouse Fort in Tilbury, Essex
Marine biologist Dylan Todd, of Twickenham, South West London, said: 'Amazing! A Beluga whale spotted feeding in the Thames. Very rare in English waters.'
Sky News presenter Kay Burley tweeted of her excitement, saying: 'We're scrambling the Skycopter. Stand by.'
A British Divers Marine Life Rescue spokesman told MailOnline: 'We've just seen on social media what's happening - we've got someone on the way now.
'We're not scrambling teams down there preparing for a rescue yet because the whale is not in distress at the moment. It seems to be freely swimming. Our only problem really is people disturbing it.
'I know people are in the water with boats, and it would be awful if it spooked it and it went the wrong way (to London).'
Lucy Babey, from conservation group Orca, told Mirror Online: 'This is the most southerly sighting of a beluga we have ever seen around these shores.
'The last sighting in UK waters was in 2015 when they were spotted near the Northumberland coastline, but they left shortly afterwards.
'Belugas usually travel in pods but this creature could have separated for a number of reasons.
'It's possible that the animal could be disorientated after becoming unwell. Storms or environmental disturbances may also have contributed.'
An RSPCA spokesman said: 'The RSPCA is aware of reports of a whale - believed to be a beluga - in the Thames.
'We are working with other agencies to monitor the situation and ready to provide appropriate assistance if requested.''He or she is obviously very lost and quite possibly in trouble. '
He urged people to give the whale 'space and minimise disturbance'.
Mr Groves said it was not the first time a beluga has been spotted in UK waters in recent years.
'In the summer of 2015 two were spotted off the Northumberland coast and one in Northern Ireland,' he said.
In 2006, a whale died after it swum up the Thames into central London despite efforts to rescue the animal.
In January 2006, an 18ft northern bottlenose whale swam up the River Thames, with thousands of people watching from the riverbank as rescuers tried in vain to save it.
The story of the whale captivated people across Britain and abroad, with it being the first time the species had been sighted in the Thames since records began in 1913.