The Blackwater River is located in the Buller District of New Zealand. It is the name given to the lower reaches of the Big River, from its junction with the Blackwater Creek to its outflow into the MÃÂwheraiti (Little Grey) River. It flows generally westwards for before turning southwards immediately prior to its junction with the MÃÂwheraiti north of the township of Ikamatua. It joins with the similar-sized Snowy River before its junction with the MÃÂwheraiti.