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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.

You can read about the latest LAWA National River Water Quality 10-Year Trend results in the National Picture tab.  Desktop and tablet users can view state and trends on the interactive map.  After you’ve learned more about the national picture, click on the Regions tab to find out more on the water quality of your favourite sites. 

Select an indicator:

  • E. coli
  • Black Disc
  • Turbidity
  • Macroinvertebrate Community Index
  • Total Nitrogen
  • Total Oxidised Nitrogen
  • Ammoniacal Nitrogen
  • Dissolved Reactive Phosphorus
  • Total Phosphorus

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LAWA National River Water Quality 10-year Trends (2009-2018)

22 September 2019

LAWA shows water quality information for 1456 river sites throughout New Zealand. Rivers are monitored for a range of water quality (chemical-physical and bacterial) indicators at 986 sites, and macroinvertebrate indicators at 981 sites by regional and unitary councils, and the National Institute of Water and Atmospheric Research (NIWA). 

Trends in river water quality have been assessed for these monitoring sites. Sites with suitable data for calculating trends over the last 10 years (2009-2018) were available for between 447 and 771 sites depending on the indicator looked at (Figure 1).

The results show a range of both improving sites and degrading sites for all indicators over the last 10 years (Figure 1). Amongst the most certain water quality trends (the dark green and dark red “very likely” trend categories), degradations were more common than improvements for turbidity, total nitrogen (TN), total oxidised nitrogen (TON), faecal indicator bacteria (E. coli) and Macroinvertebrate Community Index (MCI), whereas improvements were more common than degradations for clarity, ammoniacal nitrogen (NH4), total phosphorus (TP), and  dissolved reactive phosphorus (DRP).

 

 

Figure 1.  The proportion of sites with improving, indeterminate or degrading trends over the last 10 years (2009-2018). There was insufficient evidence to say whether water quality was improving or degrading at indeterminate sites. TN = total nitrogen, TON = total oxidised nitrogen, NH4 = ammoniacal nitrogen, TP = total phosphorus, DRP = dissolved reactive phosphorus, E. coli = faecal indicator bacteria, MCI = Macroinvertebrate Community Index. The number of sites with suitable data to determine a trend for each indicator is shown at the top of the bar.

 

Table 1. The number of sites with improving, indeterminate or degrading trends over the last 10 years (2009–2018) for nine water quality indicators.

 

 

The national aggregation of 10-year trends provides a useful snapshot of how monitored sites throughout New Zealand are tracking.  By comparing the trend results against the current state of these sites we can explore questions like “Are the worst sites getting better, or are they degrading further? How does this compare with the best sites?”.  When viewing trends by the current state (quartiles), there are no overall patterns common to all indicators, but for NH4 and DRP there is some indication that a higher proportion of the best sites (i.e., 1st quartile) are getting better (Figure 2). For TP there is some indication of a pattern of increasing proportions of degrading trends as you move from the best sites (1st quartile) to the worst sites (4th quartile) (Figure 2).

 

Figure 2.  The proportion of sites with improving, indeterminate or degrading trends over the last 10 years (2009-2018) viewed by the current state (expressed as quartiles). The first quartile represents the best water quality (i.e., the best 25% of sites), through to the 4th quartile which comprises the worst 25% of sites. Median ammoniacal nitrogen concentrations (NH4) are below detection level for many of the sites sampled so the 1st and 2nd quartiles all have the same reported NH4 concentration and therefore have been combined.  The quartile ranges for each indicator are shown in Table 2 below.

For more national level information on river water quality, we recommend the Environment Aotearoa 2019 Report.

In LAWA you can find detailed information at a site level, including monitoring results for each indicator, state by site type, and trends over the last 5-, 10- and 15-years where the data are available.  For example, at the Halswell River upstream McCartneys Bridge site in the Canterbury region, data are used to determine that total nitrogen has a very likely improving trend (reducing concentrations) over the last 10 years (2009-2018) while turbidity has a very likely degrading trend (increasing turbidity) over the same time period (Figure 3).

 

Figure 3. Water quality monitoring results, with linear trend lines fitted, for total nitrogen and turbidity at the Halswell River upstream McCartneys Bridge site (Canterbury) over the last 10 years.

 

Table 2.  State quartile ranges for river water quality indicators for all sites across New Zealand where trends were able to be calculated. (Note that high scores for clarity and MCI indicate good condition, whereas high scores for the other indicators reflect poor condition).