Ruamahanga River

The Ruamahanga River runs through the southeastern North Island of New Zealand.

The river's headwaters are in the Tararua Ranges northwest of Masterton. From there it runs firstly south and then southwest for 130 kilometers before emptying into the Cook Strait. The towns of Masterton and Martinborough are close to the banks of the river. It is joined by many other rivers, including the Tauweru River near Gladstone.

In its lower reaches, the river meanders across a large floodplain, culminating in the wetlands around the edges of Lake Wairarapa. The river once flowed into the lake, but has now has been diverted. The river drains at Palliser Bay ten kilometers further south.

Trout fishing is a popular activity and there are many swimming holes in the upper reaches.