The Ōtaki River is in the southwestern North Island of New Zealand, located in the Kāpiti Coast District It originates in the Tararua Range and flows for 45 kilometres (28 mi), heading southwest through a valley in the Tararua Ranges.

It turns northwest in the area of Ōtaki Forks, where it is joined by the Waiotauru River.

[citation needed] Around 80% of the catchment area of the river is within the Tararua Forest Park.

[citation needed] The Ōtaki River also offers fishing of brown trout and whitebait.

[citation needed] It was reported in 1863 that the river contains "what appears to be vein stones of carbonate, of lime in soft slate, are found in grade quantities.