The Buller River 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.

Westport is a town in the West Coast region of the South Island of New Zealand. Established in 1861, it is the oldest European settlement on the West Coast. Originally named Buller, it is on the right bank and at the mouth of the Buller River, close by the prominent headland of Cape Foulwind. It is connected via State Highway 6 with Greymouth, 100 kilometres (62 mi) to the south, and with Nelson 222 kilometres (138 mi) in the northeast, via the Buller Gorge. The population of the Westport urban area was 4,250 as of June 2023. The Buller District had a population of 9,670.