The English Channel is teeming with the enormous jellyfish just as thousands of people are due to visit the coast this weekend.
Port worker Clive Thomas managed to capture photos of the giant jellyfish in Portland Harbour in Dorset, while dozens more have been found washed up further along the coast in Bournemouth.
In one morning alone, lifeguards in Bournemouth recovered more than 100 jellyfish which had beached themselves.
Despite their large size, barrel jellyfish - which are called Rhizostoma pulmo in Latin - cause little harm to humans as their sting is not considered powerful. It is similar to a nettle sting and can cause a rash.
The recent influx to British shores is down to rich nutrients presently in the water which create ideal conditions for plankton to bloom.
The jellyfish are attracted towards the shore by the plankton but strong southerly winds often mean they end up being swept into the shallows.
Comment: Other freak animal births in 2015:
Portents and signs: Dog with two bodies and eight legs born on Tonga
Portents and signs: Mutant pig born with strange features and appendage in China
Portents and signs: Mutant pig born in Scotland
Portents and signs: Calf born with 2 heads at Florida farm
Portents and signs: Lamb born with face like an 'angry old man' in Dagestan
Portents and signs: 5-legged lamb born in Wales