[5][6] It rises in the Southern Alps, travelling 150 kilometres (93 mi) in a generally easterly or southeasterly direction before entering the Pacific Ocean 50 kilometres (31 mi) south of Christchurch.

Close to Mount Hutt, however, it is briefly confined to a narrow canyon known as the Rakaia Gorge.

The busiest crossing is at the small town of Rakaia, 20 kilometres (12 mi) from the river mouth, where State Highway 1 using Rakaia Bridge and the South Island Main Trunk Railway cross the river using separate bridges.

[9] It has been identified as an Important Bird Area by BirdLife International because it supports breeding colonies of the endangered black-billed gull.

Other important bird species using the riverbed are black-fronted tern and banded dotterel.