A man and his dog had a close encounter with a huge jellyfish when they went for a swim in the Percuil Estuary, near St Mawes.
The video footage features Mango, the famous surfing dog who is owned by Cornwall Wildlife Trust's Matt Slater, paddling beside the 20kg barrel jellyfish in the water.
The alien looking creatures, which can grow to up to one metre in diameter, have been causing much amazement with their appearance in our waters.
Matt, who is a marine awareness officer for the wildlife charity, also swam with the watery wonder and described it as "an otherworldly experience."
"These creatures are incredibly beautiful when you get a close look at them.
"The tentacles really look like soft coral, and round the edge of the jellyfish's umbrella like bell there is a deep blue line punctuated every twenty centimetres or so with a tiny dot, a sensory statocyst.
"Jellies are more aware of the watery world around them than you may imagine. They are constantly swimming up and down in the water column looking for profitable patches of plankton. The statocysts are their sensory cells that enable them to orientate and tell up from down."
Like a basking shark, barrel jelly fish feed exclusively on plankton which is caught with sticky mucus-covered tentacles.
They are also totally harmless to humans because their stings are too weak to get through human skin.
"Most years these larvae will perish but in years where the conditions are good, temperatures are optimal, there is plenty of planktonic food and predators do not eat them all, large numbers of them will survive creating these huge jellyfish swarms.
"It is a boom and bust cycle", said Matt.
The barrel jellies appearance also brings with it a greater chance of seeing their predators, such as the world's largest marine turtle – the leatherback turtle, which has been spotted in Falmouth Bay and Porthcurno.
And on Cornwall's north coast huge numbers of blue jellyfish have been found.
"Unlike barrel jellies blue jellies can give a mild sting so please take care around them if you find any", added Matt.
Anyone who spots a barrel jellyfish or any other marine animal can record their sighting through the Cornwall Wildlife Trust's website
