The Inangahua River flows through forest and farmland in the West Coast region of New Zealand's South Island, eventually joining the Buller River near the Inangahua settlement. It is a medium to large river, generally clear with a slight brown tinge during freshes. The river runs approximately 29 kilometres between Reefton and Inangahua Landing, with an average gradient of roughly 9.6 metres per kilometre in its upper section and a very slight gradient through the middle reaches.

The river's character changes significantly along its length. Above Reefton, the upper section has been canoed under high flow conditions from the Tobias Bridge, with most trips beginning at Branch Bridge. This section carries an intermediate recreational rating. The middle section from Reefton to Inangahua Landing is very braided across a wide river valley with a shingle bed, and is rated low for recreational value with uninspiring scenery. Below Inangahua Landing, the river is confined to a single channel between low, rocky and shingle banks, with stone blocks placed on most corners to prevent erosion, before joining the Buller at Inangahua Junction.

The upper section is described as picturesque, while the braided middle reaches are considered uninspiring. The river is not jet boated above Reefton, and swimming occurs only at Black's Point. High flow conditions appear to be preferable for paddling the upper section, as the river has been canoed and could be rafted under such conditions.

Access to the river above Reefton is straightforward, with State Highway 7 running close to the true right bank and numerous roadside access points. Below Reefton, access is more limited but available via Brazils, O'Grady, Golf Links, and Perseverance Road, as well as Landing Bridge. The right-bank tributaries — including the Waitahu River, Awarau (Larry) River, Boatman's Creek, Landing Creek, and Rough Creek — are larger and road-accessible, with the Waitahu providing a short braided shingle trip suitable for canoeists and small rafts, accessible by road 8 kilometres above its confluence with the Inangahua.