The Waimakariri River is one of the largest rivers in Canterbury, on the eastern coast of New Zealand's South Island. It flows for 151 kilometres in a generally southeastward direction from the Southern Alps across the Canterbury Plains to the Pacific Ocean.
The river rises on the eastern flanks of the Southern Alps, eight kilometres southwest of Arthur's Pass. For much of its upper reaches, the river is braided, with wide shingle beds. As the river approaches the Canterbury Plains, it passes through a belt of mountains, and is forced into a narrow canyon, before reverting to its braided form for its passage across the plains. It enters the Pacific north of Christchurch, near the town of Kaiapoi.
Instead of being unoccupied Crown land as are most New Zealand river beds, the bed of the Waimakariri River is vested in the Canterbury Regional Council.