International Mermaid Day falls on 29 March every year — a Sunday in 2026. It is an unofficial observance with no founding charter and no organising body: its first traceable outing was 29 March 2018, the night Freeform premiered its mermaid drama Siren. What has kept it going since is not the network but the folklore, the mermaiding community and the ocean causes that attach themselves to it.

What International Mermaid Day is

International Mermaid Day is a light, unofficial celebration of mermaids — in folklore, in books and film, and in the fast-growing hobby of mermaiding. It has no charter and no organising body, which means there is no programme to join and nothing to sign up for. People mark it by reading, dressing up, swimming in a monofin, or pointing the attention it generates at the sea.

It is worth being equally clear about what the day is not. No United Nations resolution created it, no government proclaims it, and no country treats 29 March as a holiday. Nor does it commemorate anything that happened on 29 March: the date began life as a broadcast slot, not as an anniversary.

Where the day comes from

The earliest observance anyone can document is 29 March 2018, the night the Freeform network premiered Siren, a drama about a mermaid coming ashore in a fishing town. In the week before, Freeform and PopSugar ran a free ticketed Mermaid Museum in Hollywood from 22 to 25 March, complete with a live performer in a 4,800-gallon tank and a 360-degree underwater projection room.

Whether the network invented the day or borrowed it is genuinely unsettled. Several calendar sites state flatly that Freeform created International Mermaid Day in late 2017 to launch the series. Freeform’s own publicity, though, describes 29 March as a date that already existed and that the premiere was timed to meet. No observance before 2018 has surfaced, which makes the network’s authorship likely rather than proven.

There is more than one mermaid day, and mixing them up is easy. National Mermaid Day is kept on 8 September by some calendars, with no traceable origin at all. The Coney Island Mermaid Parade, founded by Dick Zigun in 1983 and held near the June solstice, is older than either and is an art parade rather than an observance.

What the folklore actually says

Mermaid-like figures are genuinely old. Fish-tailed beings appear on Mesopotamian cylinder seals from the Old Babylonian period onwards. The figure usually called the first mermaid is Atargatis, or Derceto — chief goddess of northern Syria, often loosely labelled Assyrian, and by tradition the mother of queen Semiramis. The story in which she throws herself into a lake and takes a fish’s body reaches us through Ctesias around 400 BC, retold by Diodorus Siculus, and through Lucian’s On the Syrian Goddess in the second century AD.

Mermaids and sirens are not the same creature, however often the words are swapped. The sirens Odysseus was tied to the mast to survive sing from an island, and early Greek art gives them the heads of women and the bodies of birds. The fish tail arrives later, and the two figures merge properly during the medieval period. The Starbucks logo is a survival of that merge — a twin-tailed melusine of the kind popular in fifteenth- and sixteenth-century northern Europe, though the company’s story of a specific Norse woodcut is doubted by the people who have gone looking for it.

Reported sightings have a duller explanation. On 9 January 1493 Columbus logged three mermaids near Hispaniola and grumbled that they were not half as beautiful as they are painted; they were almost certainly manatees. Dugongs and seals account for others. Where nature does not explain a mermaid, showmanship often does: from July 1842 P. T. Barnum drew crowds to his American Museum with the Feejee Mermaid, a monkey’s torso stitched to a fish’s tail, an object he cheerfully admitted was a fake in his 1855 autobiography.

Mermaiding is a real job and a real sport

The professional mermaid is not a metaphor. On 13 October 1947 Newton Perry, who had trained navy frogmen during the war, opened an eighteen-seat theatre cut into the limestone below the water at Weeki Wachee Springs in Florida, and taught swimmers to breathe from air hoses while performing. The shows have run more or less continuously ever since, and the site became a Florida state park in 2008.

Amateur mermaiding turned formal in February 2021, when PADI launched a Mermaid programme with four student and three instructor ratings. The entry-level course asks only that you can swim fifty metres comfortably and float for five minutes, then teaches the dolphin kick in a monofin. Aquariums, water parks and dive shops now hire from that pool of trained swimmers.

Why ocean conservation keeps attaching itself to the day

The conservation thread was there from the start: alongside the 2018 launch, Freeform donated to Heal the Bay, which works on the water quality of Los Angeles beaches and watersheds. The link is intuitive rather than institutional — a mythical creature whose habitat is the sea makes an easy figurehead for the state of the actual sea.

It is worth being honest about the limits. No conservation programme runs under the name of this day, no measurable outcome is attached to it, and there is no organiser to hold to account. What it offers is a hook: a reason to schedule a beach clean-up, a school lesson on marine biodiversity and plastic waste, or a fundraiser on a date people already have in front of them.

How to mark the day

Celebrating International Mermaid Day needs no ticket and no costume budget. Pick one of these and do it on 29 March.