Delighted rowers were treated to the rare pleasure of sharing the River Thames with a dolphin on Thursday, August 1. 

The marine animal was spotted repeatedly breaching the water just west of Putney Bridge in West London at around midday.

However, conservationists say seeing the dolphin this far up the Thames was a "worrying" sign.

Watch: Dolphin spotted swimming in River Thames 

Mike Benson, head of rowing at Barn Elms Boat House, opposite Fulham's Craven Cottage stadium, spied the common dolphin from his office and rushed out on the water to get a closer look. 

The 31-year-old, who lives in Bloomsbury in central London, said: "I could hear some of the kids saying, 'What's that?'. 

"When I went outside I realised it was a dolphin, so I went out in one of our launches to have a play around and see what was going on. 

"We were trying to slow everyone down when passing it so it wouldn't become too distressed, but at that point everyone was more interested to see what was going on. 

"It isn't every day you see a dolphin in the Thames. 

"It would surface every few seconds, but I'm not sure if that's normal because I rarely see dolphins here. 

"There were a few builders at Craven Cottage having a look as well.  It went downriver towards Putney for a bit and came back around 4pm. 

"We think it must be lost and must be having a horrible time."

Marine mammal medics from the British Divers Marine Life Rescue are monitoring the dolphin in case it becomes stranded at any point. 

Though he frequently sees seals on the river, Mr Benson added that the last time he saw a dolphin back in 2018, the animal didn't survive. 

"We quite often get seals up this far," he said. 

"In 2018 another dolphin swam right under our boat, which was amazing. 

"But it was found dead a week later so I'm a bit pessimistic about this one's chances."

The sighting of the common dolphin comes during the 2024 National Whale and Dolphin Watch event, organised by the Sea Watch Foundation (SWF), which involves thousands of volunteers around the UK between July 26 and August 4. 

The event has already revealed a striking biodiversity of Britain’s whales, dolphins, and porpoises. 

Common dolphins are identified by an hourglass shape along the side of the body and their yellow and grey colouring. 

They are typically seen in open water in large numbers, are one of the UK’s most sociable dolphins and are often seen performing acrobatics - leaping out of the water and breaching at high speeds. 

Common dolphins are still hunted in some parts of the world and are increasingly becoming entangled in fishing gear. 

Although an offshore species, the mammals will venture into shallower coastal waters to feed; working together as a pod to herd prey into a 'bait-ball'. 

SWF outreach officer Claudia Afeltra explained: “Over the last week, we have had many common dolphin sightings - however none quite like this. 

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"These animals are open water, offshore marine mammals, rarely seen close to the shore. 

"Reports of dolphins in the River Thames are becoming more prevalent, and although exciting to onlookers, this is very worrying. 

"With this concerning sighting, we encourage all to submit any marine mammal sightings through our app, so we can better understand UK populations and can hopefully protect our species more to prevent unusual cases like this happening again. 

"This dolphin will continue to be monitored, and, hopefully, will find its’ way back to the open water."