Waikato River

The dominant underlying geology is a mixture of tephra, pumice, alluvial and greywacke. Several aspects of the river’s water quality are considered to be excellent for sustaining aquatic life (e.g. dissolved oxygen, total ammonia, pH).

Other aspects are good or better in the upper river and the hydro-lakes, but are poorer further downstream (e.g. clarity, e. coli and nitrogen)—although even then, conditions are generally better than in rivers in many other developed countries. However, concentrations of geothermal contaminants tend to be close to ecological guideline values in the upper river, but further downstream they are diluted somewhat (e.g. arsenic and boron).

Over the past 20 years there have been both improvements and deteriorations in water quality throughout the river. Continued improvements in wastewater treatment have meant that concentrations of some contaminants have declined (e.g. total ammonia and BOD). But at the same time, concentrations of nitrogen in the river have slowly increased, reflecting the ongoing increases in the many tributaries that drain areas of farmland.

At present, the main cause of concern about the water quality of the Waikato River over the next few decades is the prediction that increasing loads of nitrogen and phosphorus entering the river from larger and more intensively-used areas of farmland will increase the risk of harmful algal blooms occurring in the river.     

Waikato Regional Council and Waikato and Waipa River iwi are partners on Healthy Rivers: Plan for Change/Wai Ora: He Rautaki Whakapaipai. This project worked with stakeholders to develop changes to the Regional Plan to help restore and protect the health of the Waikato and Waipa rivers. The plan change will help to reduce sediment, bacteria, nitrogen and phosphorus entering water bodies, including groundwater, in the Waikato and Waipa River catchments. More information is available at www.waikatoregion.govt.nz/healthyrivers.