Belugas live in estuaries, continental shelves and slopes, and deep ocean basins in open water, loose ice, and heavy pack ice.
The beluga was first sighted on Tuesday near the southern Kent side of the river, downstream of Gravesend.
Conservationists said they hoped the beluga's natural instincts would soon kick in and it would head out of the estuary and back north.
"Beluga whales inhabit cold, Arctic waters off Greenland, Svalbard and in the Barents Sea", the group said.
Edna Brady from Sky News spotted the whale this morning and said it looked like it had moved a few miles further west since yesterday.
It is not clear why the whale, usually found in the Arctic, came to be in the River Thames but rescue teams are on standby in case it gets into danger.
Taking to Twitter, Andrews shared the video, writing: "Can't believe I'm writing this, no joke - BELUGA in the Thames off Coalhouse Fort".
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They are a social species, so to see one by itself in the River Thames is "concerning", he said.
It said it was ready to provide help to the whale if asked to do so by other agencies.
The WDC's Danny Groves told the UK Press Association, "He or she is obviously very lost and quite possibly in trouble". "There have only been around 20 sightings of beluga whales off the United Kingdom coast previously, but these have occurred off Northumberland, Northern Ireland and Scotland".
A female northern bottlenose whale was discovered swimming in the river in central London, going past the Houses of Parliament.
"The white body colour, absence of a prominent dorsal fin, bulbous forehead and general swimming motion all suggest this very strongly", he said.
Beluga calls variously resemble a cork being prized from a bottle or a creaking door, along with sounds described as clicks, squeaks, chirps, bleats, moans, groans, and whistles.