The Metropolitan Marine Policing Unit has responded to reports that a pod of dolphins were swimming up the River Thames in London.
According to the MPU, reports have come in that two to three dolphins are swimming up the river past Bermondsey Wall East towards central London.
They tweeted: "Just received reports of 2-3 'Dolphins' passing Bermondsey Wall East heading up river towards Tower Bridge! We are looking into this now."
The MPU later added: "The dolphins appear to be taking in the London sights whilst they wait for the tide to turn & then will make a safe return to sea."
Dolphins in the estuary of the River Thames are fairly common but they rarely travel far enough up river to reach central London.
In 2007, a report from the Zoological Society of London said there were over 100 sightings of dolphins, seals and porpoises in the Thames the previous year. However just one of these dolphins was spotted between Westminster Bridge and Tower Bridge.
The report warned that dolphins that find themselves further up river are at risk because of boat traffic.
In 2001 a 10ft bottlenosed dolphin was found dead on the banks of the Thames, three weeks after it had been spotted swimming between Wapping and Blackfriars.
Dolphins in Thames rare
Paul Jepson, veterinary pathologist for ZSL, said: "When the dolphin first appeared in The Thames, it was seen feeding and behaving normally and swimming strongly against the tide
"Over the last two weeks its condition has apparently deteriorated. At this stage, it is difficult to speculate why the animal died, but she has lost nearly all her teeth which would suggest that she is an old girl.
"It is very rare to find a dolphin in The Thames. There are two resident populations of bottlenose dolphins in the UK - one in the Moray Firth and another off the Welsh Coast in Cardigan Bay."
In January 2006, a female Northern bottlenose whale was spotted swimming up the Thames.
Experts said the whale had gotten lost and despite efforts by the British Divers Marine Life Rescue to turn the whale around back to sea, it died six days later.
A post mortem showed that the whale had died from dehydration, muscle damage and kidney failure.
The Royal National Lifeboat Institution said it was the first time it had been called to rescue a whale on the Thames.
Alison Shaw of the Marine and Freshwater Conservation Programme at London Zoo, told the BBC: "This is extremely rare in British waters as they [dolphins] are normally found in deep waters in the North Atlantic.
"It is about 16-18ft long, so is relatively mature. It is a very long way from home and we don't know why it has ended up here."