Every culture that lived beside water filled it with creatures. Some were gods, some were monsters and many were something in between: spirits that could drown you or help you depending on how you treated them. I have kept this list to beings tied to the sea, plus a few famous lake and river creatures that people often look for under “sea monsters”, and I have marked those so you can tell them apart. Where a creature has its own page on TheSea.Org, the name links to it.

A note on sources: a lot of lists online mix genuine folklore with characters invented for games and films. Everything below comes from a recorded tradition, a historical text or, in a couple of clearly marked cases, modern internet legend.

A to C

Abaia (Melanesia) — a giant magical eel that guards its lake and raises floods against anyone who harms its fish. Lake creature.

Ahuizotl (Aztec) — a dog-like water creature with a hand on the end of its tail that drags people under to drown.

Akkorokamui (Ainu, Hokkaido) — a huge red octopus-spirit of Uchiura Bay, dangerous but also revered; see Japanese sea monsters.

Amabie (Japan) — a glowing, beaked, three-legged sea creature from 1846 that foretold an epidemic.

Aspidochelone (medieval bestiaries) — a whale or turtle so vast that sailors land on its back thinking it is an island, then it dives.

Ben-Varrey (Isle of Man) — the Manx mermaid, sometimes helpful, sometimes luring fishermen.

Bunyip (Aboriginal Australia) — a creature of swamps, billabongs and waterholes. Freshwater.

Ceto (Greek) — a sea goddess of monsters, mother of the Gorgons and the Graeae.

Cetus (Greek) — the sea monster Perseus killed to save Andromeda; see Cetus.

Champ (USA) — the long-necked monster of Lake Champlain; see Champ. Lake creature.

Charybdis (Greek) — a monster that swallows the sea three times a day, forming a whirlpool; see Scylla and Charybdis.

D to H

Davy Jones (sailors’ lore) — the devil of the deep, whose “locker” is the bottom of the sea; see Davy Jones’ locker.

Dobhar-chú (Ireland) — the “water hound”, an otter-like lake beast commemorated on an 18th-century gravestone in County Leitrim. Lake creature.

Encantado (Amazon) — river dolphins that turn into charming humans and lure people to an underwater city. River creature.

Fastitocalon (Old English) — the island-whale of the Exeter Book poems, an English cousin of the Aspidochelone.

Finfolk (Orkney) — sorcerous sea people who kidnap humans to be their spouses in an undersea realm.

Funayūrei (Japan) — ghosts of the drowned who ask for a ladle to sink your boat.

Glaucus (Greek) — a fisherman who ate a magic herb and became a fish-tailed sea god and prophet.

Grindylow (northern England) — a creature of ponds and marshes that grabs children who go too near the water. Freshwater.

Hafgufa (Norse) — a monster so large it was mistaken for islands, described in the 13th-century Norwegian King’s Mirror.

Hippocampus (Greek) — a horse in front and a fish behind, pulling Poseidon’s chariot. The real seahorse genus carries its name.

Hydra (Greek) — the many-headed serpent of the Lerna marshes, killed by Heracles. Marsh creature.

I to L

Iku-Turso (Finland) — a malevolent sea monster of Finnish folk poetry and the Kalevala.

Isonade (Japan) — a shark-like monster with a barbed tail that hooks sailors off boats.

Jengu (Cameroon) — water spirits of the Sawa peoples, bringing good fortune and healing.

Jörmungandr (Norse) — the Midgard Serpent, so long it encircles the world and bites its own tail.

Kappa (Japan) — a turtle-like river imp with a water-filled dish on its head. River creature.

Kelpie (Scotland) — a shape-shifting water horse that carries riders into lochs and drowns them. Lake creature.

Kraken (Scandinavia) — a colossal many-armed monster off Norway, almost certainly the giant squid; see the kraken.

Leviathan (Hebrew Bible) — the great sea serpent of Job, Psalms and Isaiah; see sea monsters of the Bible.

Lorelei (Germany) — a siren-like woman whose song wrecks boats on the Rhine. River creature.

Lotan (Ugarit) — a seven-headed sea serpent defeated by the storm god Baal, an ancestor of Leviathan.

Lusca (Bahamas) — a part-shark, part-octopus monster of the blue holes; see the Lusca.

M to O

Makara (Hindu tradition) — a sea creature, often part crocodile and part fish, that carries the river goddess Ganga and the sea god Varuna.

Mami Wata (West and Central Africa) — a water spirit often shown as a woman with a fish tail and a snake.

Melusine (France) — a water spirit who is a serpent or fish below the waist, claimed as an ancestor by noble families.

Mermaid (worldwide) — a woman above the waist and a fish below; see are mermaids real?

Merrow (Ireland) — a sea woman whose red cap lets her live underwater.

Mishipeshu (Ojibwe) — the underwater panther of Lake Superior, painted on Agawa Rock. Lake creature.

Nereids (Greek) — the fifty kindly sea nymphs, daughters of Nereus; see Greek sea gods.

Ningen (internet, Japan) — a pale humanoid giant said to live in Antarctic seas; a modern legend.

Ningyo (Japan) — a fish with a human face whose flesh gives long life.

Nuckelavee (Orkney) — a skinless horse-and-rider demon from the sea that brings plague and blight.

Oannes (Mesopotamia) — a fish-man sage who rose from the sea to teach humans writing and laws.

Ogopogo (Canada) — the serpent of Okanagan Lake, British Columbia. Lake creature.

P to S

Pania of the Reef (Māori, New Zealand) — a sea maiden who married a chief but returned to her people in the sea; her statue stands in Napier.

Rahab (Hebrew Bible) — a sea monster representing chaos, crushed by God in Job and Isaiah.

Rusalka (Slavic) — the spirit of a drowned young woman who haunts rivers and lakes. Freshwater.

Scylla (Greek) — a six-headed monster who snatches sailors from passing ships.

Sea serpent (worldwide) — the long, many-humped monster reported by sailors for centuries; see sea serpents.

Sedna (Inuit) — the goddess of the sea and its animals, whose severed fingers became the seals and whales.

Selkie (Scotland, Ireland, Faroes) — a seal that sheds its skin to become human on land.

Sirens (Greek) — bird-women whose song lured sailors to death; see sirens vs mermaids.

Stoor Worm (Orkney) — a giant sea serpent whose body became Iceland, the Faroes and Orkney when the hero Assipattle killed it.

T to Z

Taniwha (Māori) — powerful beings of rivers, lakes and the sea, often guardians of a tribe and sometimes dangerous.

Tiamat (Babylonian) — the primordial goddess of salt water, slain by Marduk, who made heaven and earth from her body.

Triton (Greek) — Poseidon’s fish-tailed son, who calms or raises the waves with a conch.

Umibōzu (Japan) — a giant black “sea monk” that rises beside boats on calm nights.

Ushi-oni (Japan) — an ox-headed coastal demon with a spider-like body.

Vodyanoy (Slavic) — a bearded, frog-like water spirit who drowns people and keeps their souls. Freshwater.

Yacumama (Amazon) — a giant serpent called the “mother of the water”. River creature.

Zaratan (medieval Arabic and European tales) — another giant sea turtle mistaken for an island.

Which mythical sea creatures have real animals behind them?

A surprising number. Once you know the ocean, several of these legends read like eyewitness accounts that grew in the retelling.

The kraken is the clearest case: the giant squid is real, can exceed 12 metres including its feeding tentacles, and was not photographed alive in its habitat until 2004. Long, silver “sea serpents” fit the giant oarfish. The island-whale stories of the Aspidochelone, Fastitocalon, Hafgufa and Zaratan fit the sight of a large whale lying motionless at the surface, perhaps with barnacles and weed growing on its back. Mermaids and sirens were linked to manatees and dugongs as early as Columbus, and selkie stories come from places where grey and harbour seals haul out on rocky shores and stare at people with very human-looking eyes. The Abaia is a giant eel, and real freshwater eels in the Pacific can be impressively large.

Other creatures are about the sea itself rather than any animal. Charybdis is a whirlpool. The Umibōzu and Funayūrei are the fear of swamping and of weather turning without warning. Sedna explains why animals sometimes disappear from the hunting grounds. And the deep-sea legends people ask about most, such as the kraken and the Ningen, fill the part of the ocean we still know least. Having dived from the Caribbean to the South Pacific, I can tell you the real animals are often stranger than the myths; our sea monsters guide pairs 12 legends with the animals that probably inspired them.

Creature	Culture	Likely real basis
Kraken	Norse	Giant squid
Sea serpent	Worldwide	Giant oarfish, lines of porpoises, rotting basking sharks
Aspidochelone, Hafgufa, Zaratan	Medieval	Large whales resting at the surface
Mermaid, siren	European	Manatees and dugongs
Selkie	Celtic, Nordic	Grey and harbour seals
Charybdis	Greek	Tidal whirlpools in the Strait of Messina
Lusca	Bahamian	Tidal currents in blue holes; octopus and sharks
Cetus	Greek	Whale skeletons and fossil bones
Abaia	Melanesian	Large freshwater eels