The Lumaha'i River (ahupuha’a) is a river of northern Kauai, Hawaii, US. It begins in a narrow, high-walled valley in the central mountains and enters the Pacific Ocean on the northwestern coast of the island, just east of Wainiha, on the western edge of Lumaha'i Beach. Unaffected by development, its pristine waters contain populations of o'opu (Stenogobius hawaiiensis) and hihiwai (shellfish) as well as the Hawaiian coot. During heavy rainfall in winter and spring, it is prone to flooding. The Lumaha'i River Bridge traverses the waterway.