A dolphin has been spotted swimming in the River Thames in west London, a marine life charity has said.
The mammal, believed to be a common dolphin, has been nicknamed Jo Jo and was spotted swimming between the Hammersmith and Putney bridges on Thursday evening.
Mary Tester, Thames area coordinator with the British Divers Marine Life Rescue (BDMLR), said it was the fourth time a dolphin had been spotted swimming into the London stretch of the Thames this year.
She said it was "totally normal" to see dolphins in the Thames Estuary, close to the North Sea, but "when the dolphins go into London, that's something else".
Luke Denne, a journalist at the Climate Centre, said he spotted the dolphin while out filming a piece on water quality in the River Thames.
He said he was "quite surprised" to see one that far down the river.
Mr Denne then called the BDMLR which tracks dolphins and marine life that could get into difficulty.
Ms Tester said there were a "lot of different theories" on why dolphins were "coming down the river".
"It could be there are more wind farms in the North Sea which has been proven in Scotland to cause more displacement with marine mammals," she said.
She said it could also be the improved water quality of the Thames over recent years which has improved the level of fish that dolphins prey on.
"There's lots of noise in that water," Ms Tester said. "The bends and turns of the river could potentially negatively impact dolphin's echo-location."
She said the dolphins previously sighted were also believed to be common dolphins.
Ms Tester said Jo Jo was last spotted swimming towards Chelsea when they lost sight of it on Thursday evening.
While the dolphins spotted on previous occasions had died, Ms Tester said she was hopeful that a dolphin sighting in Gravesend, Kent, meant Jo Jo had returned to the estuary.
A photo of a dolphin was posted on X by the Port of London Authority (PLA) on Friday morning, with a caption that said: "PLA's rowers out on the tidal Thames early this morning encountered a neighbour in Gravesend Reach."
Ms Tester said it would be difficult to confirm it was the same dolphin as Jo Jo but it was "potentially very good news".
She added that if members of the public spot a dolphin swimming in the River Thames, or any inland waterway, they should alert the BDMLR and avoid following it in boats or canoes.
