The Pomahaka River is located in South Otago

South Otago

South Otago lies in the south east of the South Island of New Zealand. As the name suggests, it forms the southernmost part of the geographical region of Otago....

 in 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...

's 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...

. It is a tributary of the Clutha River

Clutha River

The Clutha River / Mata-Au is the second longest river in New Zealand flowing south-southeast through Central and South Otago from Lake Wanaka in the Southern Alps to the Pacific Ocean, south west of Dunedin. It is the highest volume river in New Zealand, and the swiftest, with a catchment of ,...

, flowing south for 80 kilometres from the Old Man Range of mountains to join the Clutha just north of Balclutha

Balclutha, New Zealand

Balclutha is a town in Otago, it lies towards the end of the Clutha River on the east coast of the South Island of New Zealand. It is about halfway between Dunedin and Invercargill on the Main South Line railway, State Highway 1 and the Southern Scenic Route...

. Along its path it passes the Blue Mountains

Blue Mountains, New Zealand

The Blue Mountains are a range of rugged hills in West Otago, in southern New Zealand. They form a barrier between the valleys of the Clutha and Pomahaka Rivers. They lie between the towns of Tapanui and Lawrence and rise to about 1000 metres ....

 and the forestry

Forestry

Forestry is the interdisciplinary profession embracing the science, art, and craft of creating, managing, using, and conserving forests and associated resources in a sustainable manner to meet desired goals, needs, and values for human benefit. Forestry is practiced in plantations and natural stands...

 town of Tapanui

Tapanui

Tapanui is a picturesque town in West Otago in New Zealand's South Island, close to the boundary with Southland region . A forestry town, it lies between the foot of the Blue Mountains and the Pomahaka River. Deer stalking and trout fishing are popular pastimes of the area...

 in the area known locally as West Otago

West Otago

West Otago is the local name given to part of the region of Otago, New Zealand which lies close to the border with Southland. It is administratively connected to South Otago, but is geographically separated from it by a range of hills known as the Blue Mountains.West Otago consists of rolling...

.

For a short part of its length, the river forms the boundary between Otago

Otago

Otago is a region of New Zealand in the south of the South Island. The region covers an area of approximately making it the country's second largest region. The population of Otago is...

 and Southland regions.

Major flooding of the Pomahaka in 1978 led to the relocation of the town of Kelso

Kelso, New Zealand

Kelso was a small settlement in Otago, New Zealand, located ten kilometres north of Tapanui on the Kelso River, close to its junction with the larger Pomahaka River...

 and caused damage severe enough to lead to the closure of the Tapanui Branch

Tapanui Branch

The Tapanui Branch was a railway line located near the border of the regions of Southland and Otago, New Zealand. Although the name suggests that it terminated in Tapanui, its furthest terminus was actually in Edievale...

 railway.