The Buller River is in the South Island of New Zealand. One of the country's longest rivers, it flows for 170 kilometres from Lake Rotoiti through the Buller Gorge and into the Tasman Sea near the town of Westport. As Rotoiti itself is fed by the Travers River it can be claimed that the Buller's source is at the headwaters of the Travers, on the northern slopes of Mount Travers in the Saint Arnaud Range. The Paparoa Range separates the Buller River from the Grey River.