The Barmouth Sea Monster: six schoolgirls on Llanaber beach

Barmouth, Abermaw in Welsh, sits where the Mawddach estuary meets Cardigan Bay. Along this coast, people have long told of something large in the water. In 1937 a Harlech man saw "a crocodile like animal" walking along the river bank. A local woman once found four large footprints in the sand, "as big as an elephant's". In the three weeks before March 1975, something showing "a 'square cut tail'" was reported moving fast up the main channel at Red Wharf Bay on Anglesey.

Sunday 2 March 1975. Broad daylight. Six schoolgirls, pupils at Ysgol Ardudwy in Harlech, were walking on Llanaber beach at the northern end of Barmouth promenade. About 200 yards ahead of them was a black creature.

"It was like a dinosaur," said Carys Jones and Julie Anderson. "The body of the monster was about 10ft long, with a long tail, long neck and huge green eyes." Julie Anderson remembered the feet: "like huge saucers, with three long pointed protruding nails. It was horrible." It walked towards the sea and entered the water, and the girls could still see the green eyes above the surface until the black monster disappeared into the sea.

The girls went straight to the coastguard. Coastguards said the girls were "extremely upset by their encounter." Police and the coastguard kept an alert that night, but there were no further sightings. The creature had left tracks on the beach. They were soon washed away.

Their teacher, Colin Palmer, interviewed each girl separately and compiled a drawing. It was printed as a postcard. "The interesting thing is that once the card had been circulated, it prompted other people to come forward with their sightings," Palmer said.

That week the papers carried more. Philip Wendel, a barman at the Myndon Hotel, said: "Five of us saw it going up the channel only 30 yards away." A photograph owned by Gordon Walters of Tynycoed, said to show a "strange water creature" in the Barmouth estuary two years earlier, went on display in a shop. Anglers at Black Wall had described a 10 ft long creature with feet "webbed and shaped like saucers with long protruding nails". The feet matched Julie Anderson's description.

Later retellings shifted. A 2016 article in the Cambrian News placed the sighting in the summer of 1975, in the sand dunes, and added a patrolling policeman who arrived in time to see the beast submerging. No 1975 source for the policeman has been found.

An oceanography expert from Menai Bridge suggested an otter or perhaps a seal, with a trick of the light confusing the girls about its size. The expert reportedly added: "No known creature that could have escaped from tropical waters would fit the girls' description." Writing for the Centre for Fortean Zoology in 2010, Lindsay Selby said it "sounds like the classic long necked pinniped description", though it might be "an ordinary large member of the seal family". Leatherback turtles do reach this coast, and in September 1988 the largest ever recorded washed up dead on Harlech beach. No one has proposed a turtle for the 1975 sighting. No source accuses the girls of a hoax.

Chris Barber's Mysterious Wales kept the story alive with its own version: "It had a long neck and a square face and a long tail with a flipper at the back and its skin was black and patchy." In the same years, Cornwall had its own sea serpent, Morgawr, off Falmouth. The 1975 cuttings sit in archives. The postcard and the Walters photograph have never surfaced online.