A river in the Fairy Kingdom.
The stream leads to the Fairy Kingdom. Its water sparkles. Ezmia uses it to flood the Troll & Goblin Territory in The Enchantress Returns, after already suggesting that same thing as a young fairy to solve the "troll & goblin problem". No further description of the stream given.
Trivia : Thumbelina is a fairytale by Hans Christian Andersen about a tiny girl (about the size of a person's thumb) who is wooed by toads and other small animals before finding a prince the same size as she is.