|Ministry of Magic Classification||XX|
|Appearance||horned, pale-green water-demon|
|Origin||lakes in Britain and Ireland|
|Known specimens||Grindylows in the Hogwarts lake|
|First appearance in canon||Flight of the Fat Lady (PA)|
A Grindylow is a water demon, a Dark magical creature that dwells in lakes throughout Britain and Ireland. It is a small creature of a sickly pale-green colour, with sharp little horns, long, spindly fingers and pointed, green teeth (FBAZ, PA8, GF26). Grindylows feed on small fish. They are sometimes kept as pets by merpeople (FBAZ).
During his time as the Defence Against the Dark Arts teacher at Hogwarts, Remus Lupin teaches his third-year class about Grindylows. He shows a freshly arrived Grindylow in a tank to Harry Potter when he invites the boy for tea in his office on October 31, 1993, the day of the first Hogsmeade visit. The Grindylow presses its face against the glass and makes faces and shakes his fist at Harry (PA8). When in doubt whether Harry might be an impostor after the Battle of the Seven Potters on July 27, 1997, Remus questions the boy about this event, asking him what creature sat in a corner the first time Harry entered his office. Harry correctly answers that it was a Grindylow in a tank (DH5). Grindylows also show up on the third-years' end of term exam, in which they have to wade through a pool that contains one of the creatures (PA16).
During the second task of the Triwizard Tournament, the four champions have to rescue their hostages from the Great Lake, which is populated by Grindylows. Harry is attacked by three of these creatures. They grab his ankle and robes, trying to pull him down. He shoots jets of boiling water at them with Relashio, which causes their skin to turn an angry red and allows him to escape from their grip and swim away. When one of the creatures catches hold of his foot again, Harry kicks its head, upon which the dazed Grindylow releases him and the other two shake their fists at him before they vanish. Harry later sees a pet Grindylow tied to a stake in the selkie village. Fleur Delacour is not as lucky as Harry; she is unable to fight the Grindylows who attack her and therefore fails to retrieve her sister Gabrielle from the lake (GF26).