The Tuamarina River is a North Bank tributary of the lower Wairau River with a catchment area of 102 square kilometres. The narrow valley flats are flanked by hills with heights between 600 and 1000m. The hills have a roughly equal coverage of production pine forest and native vegetation, with natives usually at the higher elevations. The river flats are dominated by pastures, which are mainly grazed by dairy cattle.
In the lower reaches, the river flows through the largest remaining wetland in the Wairau catchment, the Para Wetland. A comparatively small area downstream of the wetland has been converted into vineyard.
Regular monitoring of the Tuamarina River water quality is carried out at the bottom of the catchment just upstream of the confluence with the Wairau River. This State of the Environment monitoring has shown that water quality is in the marginal category, which is considered unacceptable unless caused by natural sources.
To identify the causes of the poor water quality ten additional sites throughout the catchment were sampled several times in 2015 and 2016.