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Waikato River

The Waikato River is the longest river in New Zealand. It starts its journey in the central North Island volcanic zone and flows into Lake Taupo. From there it continues its journey north where it flows into the Tasman Sea at Port Waikato. The catchment area is approximately 14456 square kilometres. The main stem of the river is 336km long, with about 22478km of tributaries. The catchment consists of moderately steep through to undulating topography and the river passes through predominantly pasture, with areas of indigenous forest and plantation forest. 

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

Sites 112

Monitored sites in the Waikato River catchment

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Scientific Indicators
Scientific data for this catchment

This dashboard shows information on the data collected by the regional councils for water quality indicators, analysed as state and trend.

The state for the catchment is represented by the median concentration for the parameter across all sites within the catchment and then compares that value to the quartiles for all monitored sites in New Zealand.

Click on the parameters state icons to compare this catchment with others in the region.

  • State

    State shows how the median of samples from this site compares to other sites

  • Trend

    Trend shows how the quality of water is changing over time. Depending on the sampling history duration, five and ten year timescales are available:

Can I trust this data?

The Cawthron Institute has worked alongside regional councils to verify the processes and methods used for data collection, laboratory analysis of samples collected and the statistical analysis and interpretation of the results presented.

If all Cawthron ticks are green, then you can trust this data. However, if one or more ticks are orange, then conclusions should be treated with some caution.

For more details on each tick, see our 'Can I Trust This Data?' Factsheet.

Can I trust the data?
Data Collection

All samples were collected using approved field protocols and have been analysed in accredited laboratories. Therefore the data shown here has been collected and analysed following best practice.


All samples were collected using approved field protocols and have been analysed in accredited laboratories.

Trend - Adjustment for flow

This data is not flow adjusted. National guidelines suggest that flow-sensitive variables are flow 'adjusted' before trend analysis. Therefore, any trends shown here may be affected by variations in flow across sampling occasions.


E. coli



Black disc





Total Nitrogen


Total Oxidised Nitrogen


Ammoniacal Nitrogen



Dissolved Reactive Phosphorus


Total Phosphorus

Download Data

.ZIP file of indicator readings for all sites in New Zealand

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