river in east-central South Island, New Zealand. It rises in the Southern Alps and flows 100 miles (160 km) southeast to Pegasus Bay of the Pacific Ocean, 8 miles (13 km) north of Christchurch. Fed by its principal tributaries—the Bealey, Poulter, and Esk—the river drains a basin of about 1,000 square miles (2,600 square km). The delta formed at its mouth constitutes a major portion of Banks Peninsula and part of the Canterbury Plains. In its lower course, the river flows in braided channels, which prevent navigation and limit port activities to Kaiapoi, at its mouth. During the winter, the river's upper reaches may run dry. The valley supports sheep grazing; grain is cultivated south of the river between Aylesbury and West Melton. Waimakariri is a Maori term meaning “cold water.”