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River Quality

Water is central to New Zealand’s social, economic and cultural well-being. It grows our food, powers our business and is highly valued for its recreational uses.

Click on your region to find out about the health of rivers in your area.

Click on the National Picture tab for national-level information on the condition of New Zealand's rivers.

National reporting

Ministry for the Environment and Stats NZ provide a national picture of the environment in regular reports produced under the Environmental Reporting Act 2015. Below is the overview of the freshwater domain from the Our fresh water 2017 report.

Freshwater domain at a glance

The condition of our lakes, rivers, streams, wetlands, and groundwater is important for a number of reasons. For Māori, fresh water is a taonga and essential to life and identity. Our economy depends on having plentiful water – agriculture, tourism, and hydroelectricity generation particularly rely on water. New Zealanders and tourists enjoy many forms of recreation that use our lakes and rivers, such as swimming, kayaking, and fishing. Our waterways also support many indigenous animals, plants, and ecosystems. Fresh water is primarily taken for hydroelectricity generation and irrigation for farms, and our fresh water quality depends mainly on the dominant land use in a catchment.

 

Top findings – river quality:

This summary focuses on two nutrients, nitrogen and phosphorus, which can tell us something about the risks of algal blooms; and E.coli (an indication of faecal contamination), which can tell us whether water bodies are safe for recreation.

Nutrients occur naturally and are necessary for plants to grow. However, high nutrient concentrations can result in too much growth of algae in water (this algae is generally periphyton in rivers and phytoplankton in lakes). Excessive algae in water can decrease oxygen levels, prevent light from penetrating water, and change the composition of freshwater plant and animal species that live there. High concentrations of nitrogen can be toxic to species and make water unsafe to drink.

The activities we do on the land, mainly urban and agricultural activities, can cause excess nutrients and E.coli to wash into our water bodies through run-off or filter through the land into groundwater. Phosphorus often enters surface water attached to sediment.

In urban environments, contaminants enter water bodies mainly through stormwater and wastewater networks, illegal connections to the networks, and leaky pipes, pumps, and connections.

In agricultural areas, nutrients and pathogens (organisms that can cause disease) come from animal waste and urine, and fertilisers. Since the late 1970s, agricultural practices have intensified in some areas of New Zealand, indicated by higher stocking rates and yields, increased use of fertiliser, pesticides, and food stocks, and moves to more intensive forms of agriculture, such as dairying. Agricultural land use is the world’s greatest contributor to diffuse pollution (run-off from the land or filtration through the soil). However, since diffuse discharges are hard to measure, it is difficult to determine the relationship between specific land use and water quality.

  • Nitrate-nitrogen concentration was 18 times higher in the urban land-cover class, and 10 times higher in the pastoral class compared with the native class for the period 2009–13. We classify sites by land cover: pastoral, urban, exotic forest, and native.
  • Of 175 monitored river sites in the pastoral class, nitrate-nitrogen trends were worsening at 61 percent and improving at 22 percent of sites for the period 1994–2013. Similarly in the exotic forest and native classes more sites were worsening than improving, but there were few monitored sites in these classes.
  • Nitrogen leaching from agricultural soils was estimated to have increased 29 percent from 1990 to 2012.
  • More than 99 percent of total river length was estimated not to have nitrate-nitrogen concentrations high enough to affect the growth of multiple sensitive freshwater species for the period 2009–13.
  • Dissolved reactive phosphorus concentration was 3 times higher in the urban class and 2.5 times higher in the pastoral class compared with the native class (2009–13).
  • Of 145 monitored river sites in the pastoral class, trends in dissolved reactive phosphorus were improving at 46 percent and worsening at 21 percent of sites for the period
    1994–2013. Similarly, in the urban and native classes more sites were improving than worsening, but there were few monitored sites in these classes.
  • E.coli concentration was 22 times higher in the urban land-cover class and 9.5 times higher in the pastoral class compared with the native class (2009–13). We classify sites by land cover: pastoral, urban, exotic forest, and native.
  • Of 268 monitored river sites in the pastoral land-cover class, E.coli trends were indeterminate at 65 percent, improving at 21 percent, and worsening at 14 percent of sites for the period 2004–13. Sites in the urban, exotic forest, and native classes had similar results, but there were few monitored sites in these classes.
  • Of total river segment length of large rivers, 83 percent was not expected to have regular or extended algal blooms. This is because it was modelled to either meet the periphyton national bottom line in the National Objectives Framework (60 percent) or had fine sediment (23 percent) that does not usually support algal growth (2009–13).

For more detail see: