Onlookers dialled 999 after they spotted the three mammals swimming through Tower Bridge.
Stephen Marsh, of British Divers Marine Life Rescue, told The Sun: “They could have been chasing food as the Thames is a lot cleaner nowadays.
“The route they took would be from the sea and they would have to return that way.
“The tide started dropping at 4pm so they may have started their journey back then.”
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