Which of these is a river in the South Island of New Zealand?

The Buller River is a river in the South Island of New Zealand.

One of the country's longest rivers, it flows for 170 kilometres (110 mi) 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.

The river is named after Charles Buller, Member of Parliament in the United Kingdom of Great Britain and Ireland (UK) and director of the New Zealand Company, a UK-based company in the early 1800s with a royal charter supporting colonization efforts of New Zealand. The original Maori name for the Buller, Kawatiri, is rarely used.