The Waiohine River has a relatively long and narrow catchment area of 378 sq km on the eastern side of the Tararua Range.
From its headwaters at an elevation of 1500m, the river flows out onto the alluvial gravel deposits of the Wairarapa plains, over a distance of 20km to its confluence with the Ruamahanga River.
On the Wairarapa plains the Waiohine River is joined by one major tributary, the Mangatarere, which has a catchment of 90 sq km in the Tararua foothills.
The soils of the Waiohine floodplain are formed from alluvial parent material from two different sources. The Waiohine River contributes greywacke alluvium, while the Ruamahanga River - as well as contributing greywacke - carries alluvial material eroded from Tertiary mudstones, sandstones and limestones.
The resulting deep and fertile soils of the Greytown District are among the best in the Wairarapa. Dairy farms, market gardens and domestic orchards were started soon after European settlement in the 1850s. However, some soils in the area are unsuitable for horticultural development without drainage.