The Nentir River draws its headwaters from the Winter River and Lake Nen, eventually becoming one of the greatest rivers of the known world. Easily navigable as far north as Fallcrest, the river was once traveled all the way to the settlements of Lake Nen when the river locks in Fallcrest still functioned. Today with only the small fishing village of Nenlast on Lake Nen very little trade occurs on the river north of Fallcrest.
Below Fallcrest, the river is joined by the White River and changes from the narrow fast-moving water of its origins to a much flatter, broader, and slower-moving river from then on. Indeed, the area immediately following the meeting of those two rivers is the Witchlight Fens, a maze of marshes, bogs, swamps, and otherwise difficult terrain and wandering monsters. Except for travel on the river itself, the area is almost impossible to traverse.
Eventually, the Nentir River passes beyond the Trollhaunt to the south and empties into the ocean.