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Pomahaka River

The Pomahaka River Catchment is a tributary of the Clutha River/Mata-Au and is located in southwest Otago. The river is approximately 98 km in length and has a catchment area of approximately 2060 km2.  

The Pomahaka Catchment has a long history of agricultural land use, in recent years (since the late 1990s) there as been a shift from sheep and beef farming to intensive dairy farming. The Pomahaka River is a wet, flashy, catchment and floods are common. Climate and soil type mean that farming in the Pomahaka catchment relies on artificial drainage predominantly in the form of tile and mole drains. 

The Pomahaka catchment is agricultural. The upper catchment is dominated by sheep and beef farming or forestry. The mid and lower reaches of the catchment are dominated by high intensity farming, mainly dairy. In recent years dairy farm conversions have become increasingly common in the middle and lower areas of the catchment, in particular the areas around Tapanui, Heriot
and Clydevale.

Between 1999 and 2008 the number of dairy farms increased from 38 to 105; average dairy farm size also increased from 179 to 197 hectares in the same period. Conversions are on-going.

The Pomahaka River is recognised as a regionally significant trout fishery and its largest tributary, the Waipahi, is also recognised as a fishery in its own right with the longest running fly fishing competition – the Waipahi Gold Medal, which attracts many anglers every year. Brown trout, rainbow trout, chinook salmon and perch are all found within the Pomahaka Catchment.

The Pomahaka is also recognized as being regionally significant for game bird hunting. It has relatively high bag limits and densities of mallard ducks.

The Pomahaka River is a high value river for many other recreational pursuits such as pig and fallow deer hunting, kayaking, rafting, swimming, walking, tramping, photography and art, camping, mountain biking, BBQ’s and picnicking.

Deteriorating water quality is a primary environmental concern in the Pomahaka River. This is reflected by increasing turbidity, nutrient concentrations and decreasing invertebrate community health with distance travelled from the headwaters. 

The upper Pomahaka and some tributaries such as the Leithen Burn and the upper Black Gully Stream generally have very good water quality. They are dominated by sheep and beef farming and have at least 10% forest cover. In contrast, streams with poor water quality (such as the Washpool Stream and Wairuna Stream) have the highest proportions of dairy farming (up to 79% landcover) with no forest cover.

The poor water quality can be attributed to the intensive agriculture and farm management practices that are inappropriate on the extensive tile drain network present in the Pomahaka Catchment.

Sites 7

Monitored sites in the Pomahaka 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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