Diver captures huge lion’s mane jellyfish off Wales coast 2026

Key Points

• A 21-year-old free diver and conservationist named Iestyn Morgan recorded a video of a massive lion’s mane jellyfish off Trefin Beach in Pembrokeshire.
• He described the jellyfish as being between 10 and 15 metres long, saying that it was “the length of a bus” with tentacles that extended “out of the realm of visibility.”
• According to marine biologist Dr Cathy Lucas from the University of Southampton, the lion’s mane is responsible for delivering “the worst sting” in Britain although it is harmless, recommending that one not to touch the creature and to wash their stings in warm water.
• As noted by The Wildlife Trusts, lion’s mane jellyfish can have a bell size up to 3 metres with the tentacles reaching lengths of over 30 to 36.5 metres, making them some of the longest creatures in existence.
• The lion’s mane jellyfish is normally found in waters around Scotland but is occasionally spotted in Wales during late summer and autumn months, according to Dr Cathy Lucas.
• Mr. Morgan claims that he is now seeing more tropical species in Welsh waters such as the Mediterranean triggerfish and hopes to make aquatic creatures more accessible without hurting them.

Wales (Wales Times) September 15, 2026 – A free diver has shared footage of a giant lion’s mane jellyfish spotted off the Pembrokeshire coast, prompting fresh attention on jellyfish safety and the changing mix of species in Welsh waters.

What was seen off Trefin Beach?

Iestyn Morgan, 21, from Pembrokeshire, said he was swimming near Trefin Beach when he first noticed tentacles in the water and then realised the scale of the animal. As reported by Oscar Edwards and Paul Pigott of BBC Wales, Morgan described the lion’s mane as “the length of a bus”, estimating it at about 10 to 15 metres (32ft 8in to 49ft 2in). He told the BBC: “Three turned to 10, and then to 20. They just kept on coming,” adding that the tentacles extended “beyond the range of visibility”.

Morgan said he initially thought the creature was a compass jellyfish, which is native to UK waters, before recognising it was too large. “It must have been the length of a bus or small train. I couldn’t believe how big it was,” he said, according to BBC Wales.

How large can lion’s mane jellyfish grow?

The Wildlife Trusts explain that the lion’s mane jellyfish gets its name from its long, flowing tentacles and possesses “all the beauty and bite of a lion”. They can grow up to 3m (9ft 8in) in bell diameter, while their tentacles used to catch prey can exceed 30 to 36.5 metres (98ft 4in to 119ft 8in), making the species one of the longest animals on Earth.

Dr Cathy Lucas, a marine biologist at the University of Southampton, said Morgan’s video showed the animal’s “incredible length”. She recalled that during field work in Scotland, divers would sometimes get fragments of tentacles on them even when no jellyfish were visible, because the fine filaments are hard to see. “They still sting after they break off,” she said.

Is the lion’s mane jellyfish dangerous to swimmers?

Dr Lucas told BBC Wales that while the lion’s mane’s sting is “nasty” and “the worst in the UK”, it is not considered dangerous. She advised:

“The advice is not to touch them and if you get a bit of tentacle on your skin flick it off with a stick and wash in warm water to neutralise.”

Separate reporting this summer noted painful encounters with lion’s mane jellyfish at several Welsh beaches, including Porth Dafarch, Benllech and Porth Eilian, with some people and pets affected, according to accounts collected by North Wales Live. The Irish Times reported in August that some swimmers in Dublin have begun using “sting suits” as jellyfish blooms appear in coastal waters, noting that lion’s mane stinging cells are sharper than other species and can pierce skin easily, causing painful stings. The Sun reported in August that lion’s mane jellyfish, with tentacles up to 120 feet, had been observed near Anglesey, warning of symptoms such as nausea, sweating and muscle cramps, though they are not generally life-threatening.

Where are lion’s mane jellyfish usually found in the UK?

Dr Lucas said lion’s mane jellyfish “occasionally” reach the Welsh coast later in the summer or autumn, based on public sightings records, but their main UK habitat is Scotland. The Marine Life Information Network notes that lion’s mane jellyfish are native to British and Irish waters, with encounters most likely between May and October.

Why is this sighting significant for Wales?

Morgan, who records underwater footage for social media to raise awareness about the “threats our seas are facing”, said this was the first lion’s mane he had seen in Wales. He told the BBC he is seeing “more and more” jellyfish coming into Welsh waters as he films, and described a theme of warm-water species “becoming more abundant”. He added:

“I don’t have enough summers to compare it to, but I put down a camera a few weeks ago and saw a Triggerfish, which is native to the Mediterranean.”

Morgan said creating his content has been “very rewarding” because he wants to make aquatic environments “more accessible” to people. He emphasised that he does not want to “turn it into something that I’m going out to hunt the animals or anything”, adding:

“I just get in the water, film and swim.”

Earlier in August, BBC Wales reported that Morgan regularly free dives and shares marine life footage, saying he can spend four to five hours submerged and finds it beneficial for his mental health.

What do experts say about changing species in Welsh waters?

Nation.Cymru reported in August on how marine heatwaves are changing the underwater world, noting that triggerfishtypically associated with coral reefs and tropical waters are now being seen more often by UK divers. The feature quoted divers saying that seeing a triggerfish in the UK “used to feel like a once-in-a-decade moment”, indicating a shift in species distribution. Separately, the NDTV reported in August that unusually warm weather may have contributed to increased jellyfish sightings and strandings across the UK, including large numbers of Velella velella (by-the-wind sailors) on beaches in Cumbria and Wales.

Background to this development

Lion’s mane jellyfish (Cyanea capillata) are a well-documented part of UK marine life, with seasonal appearances typically between May and October. They are more frequently recorded in colder northern waters, particularly off Scotland, but public sightings schemes have logged occasional occurrences along the Welsh coast in late summer and autumn. Recent summers have seen heightened attention on jellyfish due to painful stings reported at popular beaches, prompting local warnings and, in some areas, the use of protective swimwear. At the same time, marine biologists and divers have reported increasing observations of warm-water species in UK seas, including triggerfish and other migrants, which some experts link to marine heatwaves and changing ocean conditions.

Prediction: how could this affect coastal communities and beachgoers?

If warm-water species continue to appear more frequently in Welsh waters, coastal communities and beachgoers may see more jellyfish encounters during peak swimming months, increasing the need for clear safety advice and first-aid guidance at beaches. For local authorities and lifeguard services, this could mean more signage about jellyfish risks, updated protocols for treating stings, and possibly greater demand for protective measures such as “sting suits” in busy areas. For divers and content creators like Morgan, shifting species distributions could provide more opportunities to document marine life close to shore, supporting public awareness and conservation messaging. For tourism, the balance may be delicate: striking marine sightings can attract interest, but repeated sting incidents could deter families from swimming unless risks are well managed and communicated.