The Hangatahua River, alternatively known as the Stony River, is a river of the Taranaki Region of New Zealand

New Zealand

New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

. It is one of the larger of the numerous rivers and streams which drain the slopes of Mount Taranaki

Mount Taranaki

Mount Taranaki, or Mount Egmont, is an active but quiescent stratovolcano in the Taranaki region on the west coast of New Zealand's North Island. Although the mountain is more commonly referred to as Taranaki, it has two official names under the alternative names policy of the New Zealand...

, receiving water from streams covering most of the northwest sector of the mountain. In addition it drains the southern flank of the Pouakai complex and the alpine Ahukawakawa Swamp.
The river's upper reaches lie within Egmont National Park

Egmont National Park

Egmont National Park is located south of New Plymouth, close to the west coast of the North Island of New Zealand. It is named after the mountain which dominates its environs, which itself was named by Captain Cook after John Perceval, 2nd Earl of Egmont, the First Lord of the Admiralty who...

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The Hangatahua River forms the boundary between New Plymouth District

New Plymouth District

New Plymouth District is one of the districts of New Zealand. It includes the city of New Plymouth and smaller towns such as Inglewood and Waitara....

 and South Taranaki District

South Taranaki District

South Taranaki is a territorial authority on the west coast of New Zealand's North Island that contains the towns of Hawera, Manaia, Opunake, Patea, Eltham, and Waverley...

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The river was considered Taranaki's best trout fishery until severe erosion and land instability in the river's headwaters since 1997 caused high sediment loads.