Venomous fish with stings so powerful they can knock people unconscious have been drawn to UK beaches by climate change.
The RNLI is warning sun seekers to stay vigilant if they are planning a trip to the seaside to avoid being stung by weever fish, which are difficult to see because they hide themselves in sand.
The aggressive predatory creatures have stings capable of causing so much pain they have made grown men cry and can make people pass out.
The species, which are mostly brown and around four to eight inches long, have been reported on beaches across the UK such as in Wales, Kent, Plymouth and Cornwall.
Weever fish carry a potent venom in protective spines on their dorsal fins and gill covers which is released if someone is unlucky enough to stand on them.
Lifeguards are advising beachgoers - particularly swimmers and surfers - to wear beach shoes when in shallow waters to protect the soles of their feet from coming into contact with them.
Alternatively, paddlers should drag their feet as they walk in order to disrupt the sand and frighten off any weever fish in the sand.
RNLI lifeguard supervisor Beau Gillet said he has seen grown men cry from the power of the creature's sting.
"It really depends on the size of the fish, how you step on it and how your body reacts to the venom," he said.
The British Sea Fishing website says that the sting's effect can last for anywhere between 12 and 24 hours.
Children, elderly people, those with underlying health conditions or anyone who suffers a particularly severe reaction are advised to seek medical help if stung.
NHS guidance recommends that people who are stung should soak the affected area in "very hot" water for a minimum of half an hour to draw the venom out.
Spines that remain lodged in feet must not be touched with bare hands and should be removed using tweezers or the edge of a bank card.
Stings should not be peed on or covered with vinegar.
