Uncharted rivers (synonyms: unmapped waters, unknown rivers; example toponyms: Ueali River, the Blackwater) are rivers that have not been mapped and their routes and origins remain a mystery. Uncharted rivers are often used in narrative or game worlds with an exploration component. In fictional worlds, uncharted rivers may contain rapids, waterfalls, piranha pools, leech infested waters, and dangerous portages. They may lead into lands full of ancient temples, ruined statues, that were once occupied by ancient civilizations (or still occupied by hidden civilizations). There may be cryptids, leviathans, or monstrous beasts that dwell within the river or along its’ banks. Portions of the waterway may lead underground, through massive canyons, or into deep jungles, forests, or mangrove swamps. There may be remote abandoned outposts, forts, shipwrecks, trading posts, outfitters, fishing villages, or research facilities along the route.

Why would someone wish to travel an uncharted river? Simply to explore? There may be legends of treasure being hidden far upstream. The river may deposit clues downriver of a mineral rich land somewhere near its’ source. Or perhaps an earlier expedition or crashed plane requires rescue.

When designing uncharted rivers, consider the reason why they have never been successfully traveled. There may be obstacles or dangers preventing exploration. There may have been previous expeditions that never returned (and maybe clues of what happened to them on the river).

There are three potential important sites along an uncharted river.

• The last human settlement: Is it an outpost? A research facility?
• The transition between the known section of the river and the unknown: Is it because a falls or rapids blocks easy passage? Or does the river go underground?
• The source of the river (or destination of interest): In narratives the goal of exploring an uncharted river may be to find its’ source, or to reach some other goal thought or known to exist.