The HÃÂpuku River begins in the Seaward Kaikà Âura Range of New Zealand and flows south-east to enter the Pacific Ocean at Hapuka, between Clarence and Kaikà Âura. The name comes from the MÃÂori word hÃÂpuku or hÃÂpuka, a deep-water marine fish. Its main tributary is the Puhi Puhi River.
The first road bridge across the HÃÂpuku was completed in 1915, although the approaches were a little later. The foundations were made deeper than originally specified in order to reach a solid footing. The current State Highway 1 bridge was constructed in 1983 and is 11 spans, long, and wide. The Main North Line railway bridge was constructed in 1940 and is 23 spans of , with a total length of .
While other rivers were affected by serious flooding in 1953, the HÃÂpuku rose only at the railway bridge. Presumably this was due to the short catchment, the tectonic uplift of its headwaters and the width of the braided river bed, which is a source of railway ballast. However, an 1868 flood had more of an impact upstream, leaving a bank and a 1941 flood damaged the railway.
, two main options for the Whale Trail cycle path from Picton to Kaikà Âura to cross the HÃÂpuku River were under evaluation: either a clip-on addition to the State Highway 1 road bridge, or a new suspension bridge.
Wildlife associated with the area include black-eyed geckos, found near the headwaters of the north branch HÃÂpuku River, and bluff wetas. Banded dotterels breed in the HÃÂpuku. Introduced species include red deer, goats (kept at low levels by culling), pigs and chamois.
There were two Department of Conservation huts in the valley; Hapuku Hut and Barratts Bivvy, linked by walking tracks. However, a slip triggered by the 2016 Kaikà Âura earthquake blocked the river, with water building up behind the slip and destroying Barratts Hut and Bivvy.
Hapuka railway station was open from 13 March 1944 to 29 March 1981. A passing loop and ballast siding remain.