'Dolphin' spotted in the River Thames near Putney Bridge
Several people filmed what they believed to be a dolphin swimming in the River Thames in west London on Sunday.
The mammal, spotted near Putney Bridge, could have been a harbour porpoise according to experts.
The RSPCA said it was monitoring the welfare of the creature.
While dolphins are generally rare in London, one was spotted near the Palace of Westminster earlier this year.