To keep the public from going too close, a cordon was built around it at Red Rock Beach near Dawlish, Devon.
There may also be concerns that the massive carcass has become so bloated with gas that it may burst.
The whale is said to have been tracked in the sea for around a month but was last seen just off the coast of France.
Unusual sight: The decomposed body of the huge 50ft long fin whale washed up at the Red Rock Beach near Dawlish, Devon
Onlookers: A cordon was placed around the carcass at the Red Rock Beach to stop the public getting too close
Decomposing: It washed up ashore this morning just after 8am with a pungent smell and attracted a large crowd of onlookers
It washed up on the beach shortly after 8 a.m., with a strong odor that drew a big crowd.
Coastguards were on the scene, working with Teignbridge District Council officials to keep the area safe.
When the whale was spotted floating offshore on Tuesday, stranding investigator Robert Deaville became aware of it.
Mr Deaville, from the UK Cetacean Strandings Investigation Programme, said: ‘It made landfall this morning.
‘(It) was initially misidentified as a sperm whale. But we’ve now officially confirmed it 100 per cent as a fin whale.’
He said this was due to the black and white colouration on the plates that hang from the side of its mouth.
Taking a picture: Coastguards at the scene worked with Teignbridge District Council staff to make sure the area was safe
Found: It was identified as a fin whale due to the black and white colouration on the plates hanging from the side of its mouth
He went on to say that finding fin whales is quite rare, as they are usually found in deeper waters.
Mr Deaville said: ‘We have been monitoring stranding for 25 years and get about 600 a year.
‘That includes all whales, dolphins, porpoises etc. Out of them we get about two or three fin whales each year.’
He planned to return to the spot to collect samples in order to learn more about how the whales perished.
However, he stated that the body was so deteriorated that a comprehensive post-mortem study would be impossible.
On the sand: The discovery of fin whales is said to be very rare, with the mammals normally being found in deeper waters
Rare: This was the third stranding in Britain this year, but only the second recorded in Devon over the past 25 years
Mr Deaville added: ‘It is the responsibility of the council to dispose of it.
‘We would like to access the site and collect samples and data.
‘But then there are several possibilities of what could happen.
‘It could go to landfill either intact or cut into pieces.
‘Or it could be incinerated. They are the main methods of disposal.
‘In very isolated areas it can be buried or even left in situ.
‘But here it is a very public area.
‘So (it) will have to be moved from the beach and disposed of.
‘It is a tragedy but is something we can learn an awful lot from.
‘The fin whale is slowly recovering and we are seeing more stranding.
‘This tells us there are probably more out there which is a good thing.’
One onlooker said: ‘It’s a rather sad sight and quite an extraordinary one.
‘Apparently it’s been around for at least a month in the sea.
‘It was last spotted off France. As soon as I hit the beach I could smell it.’
Previous incident: The dangers of whale carcasses were made clear in 2013 when one exploded in the Faroe Islands
In 2013, the dangers of whale carcasses were made clear when one exploded over a marine biologist.
That 45-foot sperm whale died in November 2013 after beaching in the North Atlantic’s Faroe Islands.
The gas contained inside detonated as soon as he began ripping it open, sending organs and guts into the air.
The majority of the massive blast just missed him, and the incredible moment was captured on camera.