A 20 kilogramme jellyfish has been spotted in an estuary off the south-west coast of England.

The barrel jellyfish, said to be around one metre in diameter with tentacles two metres long, was filmed by conservationist Matt Slater.

He came face-to-face with the creature as he swam with his dog Mango in Percuil estuary near St. Mawes.

The jellyfish - which are not harmful to humans - are normally seen in deeper waters, but it is thought the mild winter has brought more plankton near to the shore.

Like basking sharks, barrel jellyfish feed exclusively on plankton which it catches with its sticky tentacles.

Mr. Slater, a marine awareness officer for Cornwall Wildlife Trust, said "It was an otherworldly experience. These creatures are incredibly beautiful when you get a close look at them. The tentacles really look like soft coral".

He added "Jellies are more aware of the watery world around them than you may imagine. They are constantly swimming up and down in the water looking for profitable patches of plankton".

The Marine Conservation Society has received reports of jellyfish being spotted across the south coast and west coast of England, as well as parts of Scotland, because of the warmer weather.

There have also been sightings of turtles in south-west England and Wales.

Matt Slater's dog, Mango, helps to give some excellent perspective on the size of the creature in the video below: