The Taramakau River is in the northwest of the South Island

South Island

The South Island is the larger of the two major islands of New Zealand, the other being the more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, to the south and east by the Pacific Ocean...

 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 rises in the Southern Alps

Southern Alps

The Southern Alps is a mountain range extending along much of the length of New Zealand's South Island, reaching its greatest elevations near the island's western side...

, 80 kilometres due east of Hokitika, and immediately below the saddle of the Harper's Pass, and runs westward for 75 kilometres into the Tasman Sea

Tasman Sea

The Tasman Sea is the large body of water between Australia and New Zealand, approximately across. It extends 2,800 km from north to south. It is a south-western segment of the South Pacific Ocean. The sea was named after the Dutch explorer Abel Janszoon Tasman, the first recorded European...

 15 kilometres south of Greymouth

Greymouth

Greymouth is the largest town in the West Coast region in the South Island of New Zealand, and the seat of the Grey District Council. The population of the whole Grey District is , which accounts for % of the West Coast's inhabitants...

.

Several small rivers are tributaries of the Taramakau, but the only one of note is the Otira River

Otira River

The Otira River is located in the central South Island of New Zealand. It rises on the slopes of Mount Rolleston in the Southern Alps, and flows north for 20 km, passing through the town of Otira before joining the Taramakau River...

, the valley of which forms the western approach to Arthur's Pass.