A river island is any exposed landmass surrounded by river water or water body.

These islands result from changes in the course of a river. Such changes may be caused by interactions with a tributary, or by the opposing fluvial actions of deposition and/or erosion that form a natural cut and meander. Nascent vegetation-free shoals and mudflats may dissipate and shift or build up into such islands through deposition; the process may be assisted through artificial reinforcement or natural factors, such as reeds, palms, evergreen trees or willows, that act as obstacles or erosion barriers, so that water flows around them.