A crowd of hundreds gathers as valiant attempts are made to rescue a young minke whale that lost its way in the Thames, despite the heartbreaking realization that all efforts would ultimately prove in vain.Onlookers on a stretch of the Thames were gripped by the fate of a baby minke whale on Monday, which had swum 100 miles out of its way but whose journey ended in disaster when it had to be put down.

First spotted on Sunday evening, the juvenile minke whale appeared to become stuck on the boat rollers near Richmond Lock and Weir, in south-west London. Crowds gathered to watch as staff, thought to be from Port of London Authority, hosed the creature down. Members of the Royal National Lifeboat Institute were greeted with cheers when they arrived.

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By 1am the whale had been captured by the British Divers Marine Life Rescue (BDMLR) so it could be assessed and seemingly saved. But the whale would not co-operate, wriggling free from the boards it was strapped to and swimming away.

A search ensued before residents upriver alerted authorities that the whale had been spotted again opposite a pub in Teddington, a quiet riverside suburb of south-west London. However, a decision was made on Monday evening that the cetacean would be euthanised because of its extensive injuries. The animal will be taken away by experts from the UK Cetacean Strandings Investigation Programme.

Julia Cable, national coordinator for the BDLMR, speaking as the animal was put down, said: “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.”

Hundreds of people had followed the animal’s journey, with one parent of young children exclaiming “it’s better than going to Seaworld!” Crowds lined the banks of the Thames, with the RNLI enlisted to make sure no one fell into the river or ventured too close to the whale on pleasure boats.

A carnival atmosphere in the sunshine slowly turned solemn as it became clear the whale was gravely injured and unlikely to survive. By mid-afternoon, it had become stuck, entangled in vines and weeds, and pushed against the brick wall of the river.

The four-metre long whale had extensive injuries from its stranding, and was young enough that it should still have been with its mother. While onlookers waited anxiously for the tide to come in, thinking enough water could refloat the whale, hope was running out.

An RNLI volunteer, enlisted to protect the whale from the crowds, told The Telegraph: “We are waiting to see if the tide comes in, but the whale really doesn’t look well. It’s stuck to the bottom.”

The whale was being bashed against the brick wall of the lock, and experts said that it was likely to have suffered damage to its internal organs as whales are not supposed to remain stationary on their bellies for extended periods of time. The young mammal had also become entangled in vines and weeds.

After being surveyed by animal experts, a decision was made to bring a vet who would assess the need to put the creature out of its misery. Police then put up hazard tape and dispersed the watching crowds.

Dan Jarvis, of the BDMLR, said any possible journey for the stranded whale to make it back to the open sea – around 30 miles away – would be too arduous for the whale. Reflecting on the likely conclusion, he said: “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.”

His colleague, Julia Cable, said the whale was “as good as stranded”, adding: “It’s not really going to come down to a rescue now. Its condition is deteriorating. It’s not acting the way it did last night. It’s basically lost any energy that it had left in it.

“It’s also got another stranding injury which along with ones from yesterday all adds up really. It’s not looking like we’ll be able to re-float the animal.”

Minke whales are the smallest of the great whales, growing to about 10 metres. 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.