The river rises as a spring in the Pureora Forest, south of Te Kūiti, on the slopes of the Rangitoto Range.

After briefly following a north-westward course, it turns south-westwards and flows for 158 kilometres (98 mi) through the Waitomo District of the King Country.

It enters the North Taranaki Bight at its mouth at the town of Mōkau.

Although the rivermouth is enclosed by a large sandbar, with a high tide, larger vessels can pass safely and enter the river, which is navigable for 37 kilometres (23 mi) upstream.

However, the risks and costs of transporting goods down the Mōkau eventually ended such enterprise.