A huge 4ft barrel jellyfish was spotted in the Helford River on Thursday in Cornwall.
But, although it looks pretty scary, swimmers do not need to worry - the giant creatures are harmless to humans.
Although it is unusual to see one so close to the shore, wildlife cruise operators have already reported hundreds of the creatures off the coasts of Devon, Dorset and Cornwall.
A number were washed up on Maenporth Beach last week, with experts saying they have been surprised by the large numbers already seen off the Cornish coast.
Thursday's was spotted by a walker just yards off the beach at Porth Saxon near the Bosloe hay meadows.
Rambler David Smith, 45, photographed the jellyfish in the rare inland sighting as he visited Porth Sawsen beach near Falmouth.
He told the Daily Mail: 'It looked at first like a giant blancmange sitting on the water. I took a closer look and realised it was one of those rare jellyfishes that are making the news."
A number of UK beaches have been invaded by these barrel jellyfish, with more predicted as the weather warms up.
A dog walker discovered one on a beach on the Isle of Portland in Dorset on Sunday.
"Although this species is harmless their numbers are likely to grow fairly quickly as sea temperatures rise.
"This is an Atlantic species and are sometimes found washed up but we still advise the public not to touch them."
Barrel jellyfish are also known as dustbin-lid jellyfish or frilly-mouthed jellyfish.
It is found in the northeast Atlantic, and in the Adriatic and Mediterranean Sea. It is also known from the southern Atlantic off the western South African coast and into False Bay.
It is also common in the Irish Sea, and is the largest jellyfish in British waters.
The barrel jellyfish a favourite food of the leatherback turtle.
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