The Taramakau River is in the northwest of the South Island of New Zealand. It rises in the Southern Alps, 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 15 kilometres south of Greymouth.
Several small rivers are tributaries of the Taramakau, but the only one of note is the Otira River, the valley of which forms the western approach to Arthur's Pass.