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Dobby: "You has to eat this, sir! Right before you go into the lake, sir – Gillyweed!"
Harry Potter: "What’s it do?"
Dobby: "It will make Harry Potter breathe underwater, sir!"
— Usage of Gillyweed[src]

Gillyweed was a magical plant that, when eaten, allowed a human to breathe underwater. It was said to resemble a bundle of slimy, grey-green rat tails. When eaten, it gave the consumer gills, allowing them to breathe underwater, and webbing between the fingers and toes, allowing them to swim underwater with ease. Gillyweed was native to the Mediterranean Sea.[1]


Harry after swallowing Gillyweed

When Gillyweed was eaten by a human, it gave them fish-like attributes, including gills to process oxygen from water, webbing between the fingers and toes for easier swimming, removing the need for blinking, and adapting to cold temperatures in water. While under the effects of Gillyweed, one could not breathe air with their lungs.[1] There was some debate among Herbologists as to the duration of the effects of Gillyweed in fresh water versus salt water,[5] but in fresh water, a sprig of Gillyweed lasted for well over an hour.[1]

Connection with Gillywater

Gillyweed was also presumably an ingredient in a drink called Gillywater. Professor McGonagall once ordered a glass of it in the Three Broomsticks Inn.[6] Romilda Vane offered Harry a glass of Gillywater spiked with Love Potion, in an attempt to get Harry to ask her to Professor Slughorn's Christmas Party.[7]


"If you ever had dreams of becoming a merperson, Gillyweed might be able to help!"
Professor Sprout to fifth year Herbology students[src]

Gillyweed was first discovered by Herbologist Beaumont Marjoribanks some time before 1845. However, the magical properties of Gillyweed remained unknown until Elladora Ketteridge ate the plant and nearly suffocated, recovering only when she stuck her head into a bucket of water.[8][9]

Jacob's sibling and Professor Sprout observing Gillyweed in Herbology

During the 1988–1989 school year at Hogwarts School of Witchcraft and Wizardry, Professor Pomona Sprout taught her fifth-year Herbology students about Gillyweed, in preparation for their upcoming Ordinary Wizarding Levels.[2]

Gillyweed in Harry Potter's hand

In February 1995, Harry Potter used Gillyweed during the Second Task of the 1994 Triwizard Tournament.[1] Dobby gave it to him,[1] after overhearing a conversation which Bartemius Crouch Junior (disguised as Alastor Moody), staged with Professor McGonagall.[10] Consuming the gillyweed allowed Harry to breathe underwater successfully in the Great Lake.[1]

Behind the scenes

  • Chocolate Frog Cards state that Majoribanks discovered Gillyweed in the mid-eighteenth or nineteenth century, while Elladora Ketteridge is said to have discovered its effects about a century earlier. This error would be fixed if the dates were switched, or if Majoribanks was alive during the same time as, or before Ketteridge, as he merely discovered the existence of Gillyweed, while Ketteridge discovered its magical effects.
  • In the video game, the Gillyweed allows Harry to breathe underwater and webs his toes. However, Harry does not have gills, nor are his fingers webbed, presumably for graphical limitations.
  • Gillyweed is featured in Magical Water Plants of the Mediterranean and Magical Water Plants of the Highland Lochs, books lent to Neville Longbottom by Barty Crouch Jnr, who was posing as Alastor Moody.
  • In the film, Neville Longbottom tells Harry about Gillyweed (he learned of it in a book Crouch/"Moody" had given him), and Harry is given the actual Gillyweed by Neville and told to put it in his mouth by Crouch.
  • In the book, it is Dobby who tells Harry about it and gives Harry the Gillyweed, after overhearing Barty's/"Moody's" staged conversation with Professor McGonagall about which tactic the Champions might use in the Second Task.
  • There seems to be some Gillyweed stored in the Herbology Greenhouses as well as Professor Snape's private potion stores.[4][11] This suggests that Gillyweed can also been used as an ingredient in at least one potion, instead of being eaten raw.
  • Gillyweed's properties along with it being indigenous to the Mediterranean might allude to a Greek myth of a mortal who ingested an herb that rendered him aquatic for the rest of his life who went on to become a minor sea god.


The Harry Potter Wiki has 11 images related to Gillyweed.

Notes and references

Blossom Degrasse · Miranda Goshawk · Quiac Marinus · Beaumont Marjoribanks · Nepali wizard · Gethsemane Prickle · Sanjay Shanker · Selina Sapworthy · Phyllida Spore · Tilden Toots · Hadrian Whittle · Sir Winogrand
Herbology at Hogwarts
Herbology Award · Herbology Lesson Cup · Herbology Race Cup · Herbology Store
Greenhouses One · Two · Three · Four · Five · Six · Seven · Professor's Office
Professors Herbert Beery · Pomona Sprout · Neville Longbottom · Unnamed Professor (19th century)
Textbooks Flesh-Eating Trees of the World · Ingredient Encyclopedia · One Thousand Magical Herbs and Fungi · Winogrand's Wondrous Water Plants
Plants studied and grown at Hogwarts
Aconite · Alihotsy · Asphodel · Belladonna · Bouncing Bulb · Bubotuber · Bubotuber pus · Chinese Chomping Cabbage · Cowbane · Devil's Snare · Dirigible plum · Dittany · Fanged Geranium · Fat cactus-like plant · Fire seed bush · Flitterbloom · Floo · Flutterby bush · Fluxweed · Gillyweed · Ginger · Hemlock · Honking daffodil · Ivy · Knotgrass · Lady's Mantle · Lavender · Leaping Toadstool · Lovage · Mandrake · Mimbulus mimbletonia · Mistletoe · Moly · Nettle · Peppermint · Puffapod · Raspberry · Rose · Sage · Screechsnap · Scurvy grass · Self-fertilising shrub · Shrivelfig · Snargaluff · Sneezewort · Sopophorous plant · Sopophorous bean · Spiky Bush · Spiky Prickly Plant · Stinksap · Sugar Shrub · Toad-eating plant · Tormentil · Umbrella Flower · Valerian · Vampiric vegetation · Venomous Tentacula · Walking plant · Wax vegetables · Whomping Willow · Wiggentree · Wild rice · Wormwood
Spells taught in Herbology at Hogwarts
Fire-Making Spell (Incendio) · Herbivicus Charm (Herbivicus) · Incendio Duo Spell (Incendio Duo) · Lumos Solem Spell (Lumos Solem) · Severing Charm (Diffindo)