Strange footage has emerged online this week of a large, dark shape surfacing in the River Thames.
The peculiar video, which was uploaded on to YouTube and sent to us via e-mail, was recorded on a mobile phone by someone riding on the cable car in Greenwich, London back on March 26th.
Set against the backdrop of the Millennium Dome, the footage shows a large black shape rearing out of the River Thames before disappearing again, leaving a momentary disturbance in the water.
"Are there whales in the Thames ?" the uploader asks. "Or is it some weird submarine ?"
Whether the video shows something genuinely unusual in the water remains unclear, especially given how easy it would be to fake something like this using video editing software.
To read more and view the video, click here.