Grindylows are just one of the creatures that live in the lake at Hogwarts. As well as roaming the lake freely, some Grindylows are kept as pets by the merpeople. Several of the Grindylows in the lake attempt to prevent Harry from progressing in the lake by gripping his ankle with their strong fingers. Harry manages to escape their clutches with a combination of the spell Relashio, and by kicking at them. Fleur Delacour was attacked by Grindylows on her way to find her hostage, and was prevented from reaching her sister by the creatures.