River Thames: Is this a shark swimming in London's waterway?

Is this a shark swimming in the River Thames in London?

Video footage, taken on 22 July, shows what appears to be a fin moving through the water near Hammersmith Bridge.

The Port of London Authority said the Thames had an "abundance of aquatic life with occasional visits from dolphins, porpoises and even whales".

But, it said, it was "unlikely that any sharks would swim that far upstream".