The Wainui River is a river of the Tararua District in the Manawatà «-Whanganui Region of New Zealand's North Island. It rises on Mt McCartie and flows approximately southeast through isolated hill country to reach the Pacific coast at Herbertville, five kilometres west of Cape Turnagain. The name Wainui means large waters. It is derived from the MÃÂori words wai meaning water and nui meaning large.
The Wainui River has a number of small tributary streams. Tributaries include (west to east): Angora Stream, Wimbledon Stream, Waikopiro Stream, Mangaone Stream, Mangaohau Stream, Tapui Stream, and Wairauka Stream.