The Pomahaka River is in South Otago in New Zealand's South Island. It is a tributary of the Clutha River, flowing south for 80 kilometres (50 mi) from the Old Man Range / Kopuwai mountains to join the Clutha about 15 km west of Balclutha. Along its path it passes the Blue Mountains and the forestry town of Tapanui in the area known locally as West Otago.