Marine experts are urging tourists scared of jellyfish stings not to be put off visiting Welsh beaches.
The lion's mane jellyfish is less common and has a nasty sting
Fears were raised by reports of Spanish holiday beaches being closed as thousands were treated for stings.
The conservation charity Sea Trust says that although hordes of jellyfish are being sighted, people should not panic.
"Most 'jellies' that we find in our waters are pretty innocuous and give nothing more than a nettle-type sting," said chairman Cliff Benson.
"We see large numbers every summer. We live in a nice little cul-de-sac of the North Atlantic and it's very productive so there are several species of jellyfish.
"It's just a matter of keeping your eyes open and just not bumping into them if you can avoid it."
Mr Benson, who runs Sea Trust from Pembrokeshire, said he was keen that beach-lovers should not stay away from Welsh coasts just because of isolated reports of people being stung.
"Don't panic," he said. "It's a matter of keeping all this in perspective - one person may have been stung, but 500,000 or 1m have not.
Harmless moon jellyfish often float in "rafts"
"There is enough of a problem getting kids out and about these days. You don't stop your kids playing outside just because they get stung by a nettle or a bee or a wasp, so why keep them away from the beach?
"Just come to the coast and have a great time. I was paddling with my grandchildren yesterday, catching shrimps, and we had great fun."
Medical experts advise treating minor jellyfish stings with vinegar, to kill off the stinging cells. More serious injuries should be seen by a doctor, however.
The Marine Conservation Society has received reports of hundreds of thousands of jellyfish being washed up on Welsh beaches this year.
The lion's mane is Britain's largest species. It can be up to 2m wide, is the traditional jellyfish shape, and is bright reddish-brown.
More common, however, is the harmless moon jellyfish. In June around 1,000 came ashore at Blackrock sands in Morfa Bychan, near Porthmadog.