For anyone twitching the Beluga it's been feeding around the barges for the last hour and hasn't moved more than 200m in either direction.
The beluga's appearance brings back memories of the famous 2006 Thames whale.
However rescue teams were on standby in case the animal, which is normally found thousands of miles away in the Arctic, gets into danger.
They are a social species, so to see one by itself in the River Thames is "concerning", he said.
A "very lost" beluga whalespotted in the Thames on Tuesday has been sighted again.
"Beluga whales are an Arctic species, often seen in groups".
"Hopefully instinct will soon kick in and the beluga will leave the estuary and go out into the north sea and then head north where it should be", the scientist explained.
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Beluga whales were last spotted in the United Kingdom three years ago off the coast of Northumberland and Northern Ireland, but sightings were "extremely rare", spokeswoman Julia Cable said.
The animal welfare group says it is ready to provide help to the whale if asked to do so by other agencies.
After British Divers Marine Life Rescue were alerted, they confirmed the sighting, noting that the whale seemed to be "swimming strongly".
"If they are eating things like jellyfish, we don't tend to have a great deal of jellyfish in the Thames, but we do have quite a lot of plastic bags, which could be quite an issue", she said, BBC News reported.
We would encourage people to look from the land if the whale is still close to the coast.
Belugas, which can grow up to 5.5 metres (18 feet) long, spend most of their time off the coasts of Alaska, Canada and Russian Federation, though they often travel great distances in search of food.