YouTube user Penn Plate uploaded the shaky video, which appears to show a large underwater object just under the surface of the River Thames in front of the Millenium Dome.
Commenters on the video sharing site have suggested it may be many things; from the Loch Ness Monster holidaying in London to a Russian submarine on patrol.
The video was shot from the Emirates Air Line - a cable car service near the Greenwich area of London famous for the views across Greater London.
Since being uploaded on 27 March, the video has recorded over 775,000 views and more than 270 comments in its short time online.
An increased number of dolphins, porpoises and seals have been spotted in the Thames over the years as the fish population has increased. In 2006, a northern bottlenose whale died of dehydration and muscle damage in the Thames after getting lost en route to the Atlantic.