river in east-central South Island, New Zealand. It rises in the Lyell and Ramsay glaciers of the Southern Alps near Whitcombe Pass. The river flows east and southeast for 90 miles (145 km) before entering Canterbury Bight of the Pacific Ocean through a delta just west of Banks Peninsula. Fed by its principal tributaries, the Mathias and Wilberforce, the river drains a basin 1,000 square miles (2,600 square km) in area. Its lower course crosses the Canterbury Plains, where the river flows in braided channels too shallow for navigation. The name Rakaia (Maori for “to arrange in ranks”) may refer to an ancient method employed in fording the stream.

At the sawmilling town of Rakaia, 13 miles (21 km) upstream, the chief South Island rail and road lines cross the Rakaia River on mile-long bridges. Deposits of fine, windblown loess on the lowlands along the lower course yield grain crops, and salmon are taken from the stream. There are hydroelectric stations at Lake Coleridge, and a canal at Highbank brings water from the Rangitata River for hydroelectric generation and irrigation.