It flows for 151 kilometres (94 mi) 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.

[5] The source of the Waimakariri is located in the Southern Alps, at the head of a valley to the west of Arthur's Pass, where it is primarily fed by snow melt and glacial runoff.

As with other braided river systems, the main channels frequently change within the primary riverbed, especially during periods of high flow rates.

[7] The river currently reaches the Pacific Ocean just to the north of Christchurch, entering Pegasus Bay by way of Brooklands Lagoon.

[8] Download coordinates as: Due to the size of the river, only a limited number of bridges cross the Waimakariri.

[11] As one of the largest rivers on the Canterbury plains, the Waimakariri is an important habitat for wildlife, including many endangered species of plants and animals.

The dry sections of riverbed are home to black-fronted terns, where braids in the river provide a natural barrier to predators.

It received support from the community but the dam was never built since the Government offered inexpensive electricity from the Lake Coleridge scheme.

[23] Some of the pollution was caused by liquid wastes from industries such as a meat processing plant and wool scourers in the vicinity of the river.

Her poem "After Flood", published under the pseudonym "Paul Henderson", describes "the alive / Roar of the river loud on the loose", and as being an "age-long wanderer, age-wily".

[25] Her novel, Ice Cold River (1961), describes the flooding of a family farm at Christmas after the Waimakariri River bursts through a stopbank:The water advanced so slowly and quietly that it seemed no more than the tide making in an estuary backwater.... [Q]uite suddenly, the lake of water seemed to lift itself, hurled itself over the garden and against the house in a wave that thumped as did a blasting operation at a distance.

Immediately the house was surrounded, and the wave went on, eating up the fields with rapid teeth of dirty foam, in which sticks and grass and debris turned over, were engulfed, and reappeared in an endless sucking whirlpool.