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The Whanganui River is the country’s third longest river and its longest navigable river. Beginning on the northern slopes of Mount Tongariro it flows north-west until it turns south-west at Taumarunui. It then flows down through the King Country before turning south-east and flowing past the settlements of Pipiriki and Jerusalem until it reaches the coast at Whanganui.

The Whanganui is the ancestral river to the Whanganui iwi (Te Āti Haunui-a-Pāpārangi), a confederation of three ancestral groups: Hinengākau of the upper river, Tama Ūpoko of the middle reaches and Tūpoho of the lower Whanganui.

According to Māori legend, the Whanganui River was named by Hau who set off from Patea following his wife Wairaka along the coast. The first obstacle Hau met was a great river flowing westwards to the setting sun. He sat to consider the best way to cross the water and uttered these thoughts: “Too wide to swim, too deep to wade. I will wait for the tide to turn”. That was how he named the river Whanganui, which literally means the ‘big wait’.

Despite many stretches of white water and more than 200 rapids, the Whanganui River has always been an important communication and transport route for both Maori and European settlers. Before Europeans arrived, the Whanganui area was one of the most densely inhabited in New Zealand and colonial settlers later used the area near the river’s mouth as a major trading post.

Today, more than half the catchment is covered in native bush or forest and approximately a third of the land area is used for sheep and beef farming. The biggest urban area is the coastal town of Wanganui which has a population of about 42,500.

There is weekly monitoring in place at Town Bridge. See the Horizons website for details.

Sites 17

Monitored sites in the Whanganui 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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