The Sea and Little Fishes is a short story by Terry Pratchett, written in 1998. It is set in his Discworld universe, and features Lancre witches Granny Weatherwax and Nanny Ogg. It was originally published in a sampler alongside a story called "The Wood Boy" by Raymond E. Feist, and later in a collection called Legends.
The story established a basis for various elements of the novel A Hat Full of Sky, but is not required to understand that novel.