What is the weird creature filmed swimming in London's Thames?

A mysterious creature has been filmed emerging from murky water in London's River Thames.

A worker from the University of Greenwich spotted the strange marine life from a distance before filming it disappear into the depths of the river.

'I was at work today, I'm about the eighth floor up when me and my workmate noticed a weird fin-like object coming up and down and making some weird swirls in the water,” the man wrote alongside the video on Twitter.

“We kept our eyes out for about five minutes and it came up again right by the shore. And then it disappeared again.”

The worker spotted the strange creature from the eighth floor. Source: Twitter
In an instant, it disappeared. Source: Twitter

The bizarre sighting comes one year after a similar mysterious sea creatures baffled marine experts, who admitted they had no idea what the animal could have been.

A passenger on a cable car in Greenwich recorded the video out of the window, capturing a large mass moving under the surface.

Two fins could be seen appearing to break the surface, as if the creature is coming up for air, before the dark shape disappears beneath the murky depths.

“We are not aware of anything that large and moving in the Thames,” Ian Tokelove from the London Wildlife Trust said at the time.