The Allen River is a river in the West Coast district 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 drains the south side of the Allen Range (heights up to 1,450 m) which forms part of the boundary between West Coast and Tasman districts.
The river has left and right branches for half its length, and the right branch has a major tributary stream in a valley between the two branches. The united river flows south through a narrow gorge and is joined by the Johnson River 200 m upstream of its confluence with the North branch of the Mokihinui River

Mokihinui River

The Mokihinui River is a river located on the West Coast of New Zealand's South Island, about 40 kilometres north of Westport.- Geography :The Mokihinui River's headwaters are located in the Glasgow Range and its mouth is on the Tasman Sea...

.