A baby minke whale stuck in the River Thames has been euthanised “to end its suffering”, rescuers have said.
The animal was first spotted on Sunday but its condition has “deteriorated rapidly”, the British Divers Marine Life Rescue (BDMLR) said.
Hundreds of people gathered at Teddington Lock in south-west London on Monday to catch a glimpse of the whale.
Measuring between 10ft (3m) and 13ft (4m) long, it was first seen at nearby Richmond Lock stuck on boat rollers.
The animal was then rescued from there but escaped, before becoming stranded again.
The BDMLR said on Monday evening that a decision had been taken to “euthanise” the minke.
The equivalent of a post-mortem examination to establish where it came from and what may have happened will be carried out in the future.
A statement said: “The juvenile minke whale in the River Thames at Teddington Weir has deteriorated rapidly over the last couple of hours of monitoring by BDMLR Medics and representatives from Cetacean Strandings Investigation Programme, based at the Zoological Society of London.
“The animal is positioned against the river wall and the tide is now dropping quickly and it is expected the animal will be beached very soon.
“BDMLR medics will try to position themselves to prevent the whale entering deep water again where it is now having difficulty swimming as its strength reserves seem to be compromised.
“Once the whale is beached a veterinary team will be on stand by to euthanise the animal to end its suffering, in the meantime the team will continue to do what they can to care for the animal under these sad circumstances.”
Julia Cable, national coordinator for the BDLMR, added at the scene: “The vets are here from London Zoo – they will give the whale a large anaesthetic which will put it to sleep, it shouldn’t feel anything.
“It’s always sad but we know putting it back into the open sea would’ve been sending it to starve.
“It’s nutritionally in a poor state, it has run out of energy and will be dehydrated and starved.
“It’s been separated from its mother or a group and will definitely be socially dependant.
“We tend to see one whale per year in The Thames. It’s not that common and hopefully it won’t be.
“It’s come in from the Thames Estuary. For a whale to come this far up and not be seen until it was in the Hammersmith area is unusual.”
Minke whales are the smallest of the great whales, growing to about 33ft (10m).
They can usually be found throughout the northern Atlantic and Pacific Oceans.
Their range extends from the ice edge in the Arctic during the summer to near the equator during winter.
Videos on Sunday showed the juvenile being hosed down by a man believed to be from the Port of London Authority, while a vet performed a check-up at the river’s edge.
The Royal National Lifeboat Institute then arrived at the scene to the cheers of onlookers at about 9pm.
Fire crews were also at the scene, along with the BDMLR.
The whale was found to be in poor health and was put on pontoons to make it more comfortable on Sunday night as it was decided then that it should be put to sleep.
But it managed to get free and back into the river.
It then made its way to Teddington Lock, and its condition worsened the day progressed on Monday.
Reflecting on the outcome, Dan Jarvis, welfare development and field support officer at the BDMLR, said: “This is likely the case with stranded cetaceans.
“It’s for a very good reason they’ve come ashore.
“Sometimes it is by accident, they do get stranded, but usually sadly it is the case that they’re already seriously ill or badly injured.
“And there’s not a great deal we can do in that situation.”
Families had spent the entire day waiting for good news on the animal but were left deflated by the sad outcome.
The whale had visible, bloodied scratches all over its body from being trapped on the riverbed, in vines and against a wall.
Onlooker Patrick Owens, 67, from Teddington, said: “I feel very conflicted about it all.
“I mean we’re here watching as this animal struggles, it feels ghoulish, but we’re here because it’s obviously very unusual for there to be a whale in Teddington.
“People have become very invested in it all day but that interest has bow turned to sadness.”
Another onlooker said: “It’s incredibly sad, we’ve been rooting for it to survive all day.
“I feel so sorry for how it has struggled for so long.”