Gillyweed is a magical plant native to the Mediterranean Sea. When it is eaten by a witch or wizard, one grows gills and webbing between the fingers and toes, allowing them to process oxygen from water and navigate underwater more easily. There is some debate among Herbologists as to the duration of the effects of Gillyweed in fresh water versus salt water,[1] but the effects of Gillyweed in fresh water seem to last about an hour.


Gillyweed is said to resemble a bundle of slimy, grey-green rat tails.

Known Uses

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Harry after swallowing Gillyweed

Harry Potter used Gillyweed during the Second Task of the 1994 Triwizard Tournament. Dobby gave it to him, after overhearing a conversation which Barty Crouch Jr, disguised as Alastor Moody, staged with Professor McGonagall.

Connection with Gillywater

Gillyweed can also, presumably, be used as an ingredient in a drink called Gillywater. Professor McGonagall once ordered a glass of it in The Three Broomsticks. Romilda Vane offered Harry a glass of Gillywater spiked with a Love Potion, in an attempt to get Harry to ask her to Professor Slughorn's Christmas Party.

Behind the scenes


Gillyweed at Harry Potter's hand

Gillyweed in Harry Potter's hand

Notes and references