The Hurunui River is located approximately 90 kilometres north of Christchurch in North Canterbury, New Zealand. Some 150 kilometres long with a total catchment area of 2,671 square kilometres, it has two main branches originating east of the Main Divide in the Southern Alps. The north branch draws predominantly from Lake Sumner, a remote high country lake, while the south branch originates in the Southern Alps. The river is considered the most important river in Canterbury for paddlers, offering navigable flows year-round and a variety of whitewater runs catering to all ability levels.

The river is typically described in three sections. The upper reaches run from Lake Sumner down through a sub-alpine valley, passing through tight rocky gorges interspersed with open boulder gardens. Key segments include the Sisters Gorge (Grade II), the Jollie Brook section (Grade II), and the popular Top Gorge. The middle section includes Maori Gully (Grade III, approximately 2.5 kilometres), which becomes Grade IV above 100 cumecs. The lower Hurunui (Grade II, approximately 10 kilometres) offers an easy wide gorge with corner and bluff-style rapids, with a put-in at Cat Hill Station (access permission required) and take-out just below the State Highway 1 bridge.

The gauge at Mandamus is the standard reference point. Low flow is around 15 cumecs, 25 cumecs is comfortable paddling, 30–40 cumecs is considered a good standard flow, and above 100 cumecs Maori Gully grades up significantly. Flooding can occur regularly throughout the season, affecting access and safety.

Access to the upper river is via State Highway 7 through Waikari and Hawarden, then along Lake Sumner Road. The Balmoral Bridge on State Highway 7 provides access to the middle section. Notable hazards on the lower sections include the "Eddy of Doom" on the Dozy Stream to Seawards run — a large recirculating eddy below a long straight stretch where the river flows directly into a bluff; less experienced paddlers are advised to take the right-hand line to avoid it.

The upper reaches are a controlled fishery managed under special access rules. The river and surrounding area also support blue duck and braided river bird species in the headwaters and tributaries. Packrafting and bikerafting are increasingly popular on the upper river, in addition to traditional kayaking and rafting. Lake Sumner and Loch Katrine, connected by a natural canal, are suitable for sailing and boating, with Loch Katrine accessible by 4WD only.