A small whale stranded along the River Thames is unlikely to survive and make it back to the open sea, rescuers have said.

Crowds gathered at Teddington Lock in the south-west of the capital on Monday to catch a glimpse of the whale, a minke between 10ft (3m) and 13ft (4m) long.

It came after hundreds of people gathered at Richmond Lock and Weir on Sunday after the animal became stuck on the lock’s boat rollers.

Videos showed it being hosed down by a man believed to be from the Port of London Authority (PLA), while a vet performed a check-up at the river’s edge, before the Royal National Lifeboat Institute (RNLI) arrived at the scene to the cheers of onlookers at about 9pm.

Fire crews were also at the scene, along with the British Divers Marine Life Rescue (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.

Julia Cable, national co-ordinator of the BDMLR, said the whale is now completely stationary in the water up against a wall in the area of Teddington Lock.

She told the PA news agency the animal is “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.

“We’re just going to make it a little bit more comfortable and we’re going to have a veterinarian come down and take another look at it, and then they’ll make a decision.

“It’s not looking like we’ll be able to re-float the animal.”

Dan Jarvis, welfare development and field support officer at the British Divers Marine Life Rescue service, said the veterinarian will carry out a health assessment on the whale.

He told the PA news agency: “From the assessment that we gave last night we already know the animal’s in poor nutritional condition which doesn’t have a good prognosis, so in all likelihood the animal would be put to sleep to prevent further suffering in this case.”

Mr Jarvis said the rescuers work in conjunction with the Cetacean Strandings Investigation Programme (CSIP) which carries out post-mortem examinations.

He said they are likely to need help from the Port of London Authority to make arrangements for the removal of the whale.

Mr Jarvis said it would be a long journey for the stranded whale to make it back to the open sea, around 30 miles, and logistically a big task.

He said the whale was put on pontoons to make it more comfortable on Sunday night as it was decided then that it should be put to sleep.

“It actually managed to get free of the pontoons unfortunately and back into the river,” he said.

Reflecting on the likely conclusion, Mr Jarvis 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.”

The whale was spotted near Teddington Lock just after 10.20am on Monday, heading downstream towards Chiswick and back towards Richmond Lock and Weir.

Pictures showed passers-by and photographers lining the river on Monday afternoon, with the whale clearly visible in the water.

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.