Large numbers of potentially fatal Portuguese man-of-war have washed up on a Cornish beach prompting its closure.
RNLI lifeguards erected do not swim red flags at Perranporth beach earlier because of the “unusually large number” of the man-of-war.
The jellyfish-like creatures with long purple tentacles have been seen in Cornwall and Wales this month says the Marine Conservation Society (MCS).
With mild sea temperatures of 16C there were fears of swimmers being stung.
The RNLI said it placed red flags at Perranporth beach “for a short time” earlier to signal that the water was out of bounds, while lifeguards took advice on the level of danger to beachgoers.
It said the beach had reopened by 15:13 BST.
Man-of-war were spotted at Newgale, Pembrokeshire, on 8 September and the next day on beaches near the holiday destination of Newquay.
They have also been seen at Porthmelon Beach on the Isles of Scilly and on the Cornish beaches of Portheras Cove and Summerleaze, Widemouth, Perranporth, Hayle, Holywell Bay and Praa Sands.
Six were reported at Gwithian.
Dr Peter Richardson from the MCS said a man-of-war’s tentacles which are about 10m (30ft) long, “deliver an agonising and potentially lethal sting”.
“They are very pretty and look like partially deflated balloons with ribbons but picking one up could be very nasty,” he said.
The man-of-war retain their sting when they are wet, even if they look dead, he warned.
He advised anyone who was stung to get the tentacles away from the body as soon as possible.
Leatherback turtles have also been washed up because of an increase in jellyfish which they feed on, Dr Richardson said.
A leatherback turtle was found at Portreath on 9 September and another one has been reported in Pembrokeshire.
If symptoms become more severe, or a sensitive part of the body has been stung, you should seek medical help.
The MCS is asking people to report any sightings which could rise as man-of-war are driven across the Atlantic by recent storms.