A member of the Shad Thames Residents Association (STRA) seen the frightened animal floating alongside Saint Saviour’s Dock, close to Tower Bridge, on Saturday.
It is believed the fox jumped or fell onto the boat rom the docks above.
It was rescued by the London Fire Brigade, who managed to coax it right into a cage and carry it to land.
The STRA stated on Twitter: “An enormous thanks to the London Fire Brigade and RSPCA for saving a bit fox who determined to take a boat trip in St Saviour’s Dock.
“You have been all good.
“A truly lovely display of care and kindness.”