The Ahaura and its many tributaries rise in the Lake Sumner State Forest park and enters the Grey River at the small settlement of Ahaura approximately 30 km upstream from Greymouth.

It drains a huge area of land and in its lower reaches below the Haupiri confluence can have a tea-colour stain for much of the year.

The Ahaura in the gorge is a wide, fast, shallow, braided river, with extensive grassy flats, surrounded by beech forest.

[8] Gold digging started about 1865[9] and a small settlement of shanties had been built at Ahauru by January 1866.

[12] The Ahaura Terraces and Nancys Clearing Ecological Areas were declared in 1997 to protect kahikatea and red beech (tawhai raunui) forests on the river's terraces, including kākāriki parakeets.