The Buller River (Māori: Kawatiri) is a river in the South Island of New Zealand. The Buller has the highest flow of any river in the country during floods, though it is only the 13th longest river; it runs for 177 km (110 mi) from Lake Rotoiti through the Buller Gorge and into the Tasman Sea near the town of Westport. A saddle at 710 m (2,330 ft) separates the Buller from the Motupiko River and that is divided from the Wairau River by a 695 m (2,280 ft) saddle, both aligned along the Alpine Fault, as is the top of the Buller valley.
Within the Buller Gorge and downstream from the Deepdale River joining, the Buller crosses from Tasman District into Buller District. The Paparoa Range separates the Buller River from the Grey River. A number of flora and fauna are found in the Buller catchment, many of these extending onto the slopes of the Paparoa Range.