The Clarence River is a major river which flows through the Kaikōura Ranges in the northeast of New Zealand's South Island. At roughly 209 kilometres (130 mi) long, it is the longest river in Canterbury and the eighth longest in New Zealand.

The South Island, also named Te Waipounamu in Māori, is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, and to the south and east by the Pacific Ocean. The South Island covers 150,437 square kilometres (58,084 sq mi), making it the world's 12th-largest island, constituting 56% of New Zealand's land area. At low altitude, it has an oceanic climate.