WATCH out – the bane of all sea bathers is back with a vengeance.

With the weather warmer and English Channel water temperatures rising, experts say conditions are ripe for an unwanted baby boom.

For the Marine Conservation Society (MCS) says bathers heading to Hampshire beaches could be dipping into a “jellyfish soup”.

Breeding conditions mean the spooky see-through sea creatures will be having their day in the sun.

In particular, the society fears massive blooms of mauve stinger jellyfish, which it says has already left large numbers of people this year requiring treatment for stings around the coast of Malaga in Spain.

Other types spotted locally in recent summers are blue jellyfish, measuring up to 12in wide, and moon jellyfish.

Portuguese man-of-war – a jellyfish- like creature with a potentially fatal sting – have also been seen on occasion.

Peak season is between July and early September. MCS biodiversity programme manager Dr Peter Richardson said: “The rise of the jellyfish is telling us that we must take better care of our seas.

“There is now strong evidence that jellyfish blooms are increasing in some parts of the world and this has been linked to overfishing and pollution, while climate change may also be affecting the seas in their favour. They are the thermometers of the oceans because jellyfish populations are indicators of the health of our seas.”

The true scale of the jellyfish explosion may have been masked by the unusually cold summer.

But Mr Richardson said: “Jellyfish are great opportunists and take advantage if the conditions at sea are favourable to them.”

More than 7,000 significant jellyfish sightings have been reported in the British Isles since the MCS launched its survey in 2003.