The Swamp of the Black River is a large natural area a few days' journey from the Valley of the Mystics. It has a boggy floor, and is filled with all kinds of diverse plants and animals. Unlike plants and animals on Earth, some plants here are capable of locomotion, and some animals are stationary. Many plants here resemble lifeforms found on coral reefs.
The Swamp is where Jen meets Kira and Fizzgig for the first time. Fizzgig frightens Jen so that he falls into a muddy bog, but Kira calls a Nebrie who appears from under the bog and pushes him out.