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.
Regular water quality monitoring by New Zealand’s Regional and Unitary Councils, supplemented with NIWA data, means there’s water quality information for around 1,400 river sites. You can read about the latest LAWA National River Water Quality 10-Year Trend results in the National Picture tab. 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.
1 November 2018
Trends in river water quality have been assessed for nine water quality indicators for sampling sites all around the country over the last 10 years (2008-2017)1. This year, LAWA reports 10-year national trends for the Macroinvertebrate Community Index (MCI) for the first time. Suitable data2 were available for between 392 and 673 sites depending on which water quality parameter you look at. The analysis included sites where samples were collected monthly, bimonthly or quarterly for chemical-physical and bacterial river water quality indicators and annually or twice per year for MCI.
LAWA reports five trend categories (very likely improving, likely improving, indeterminate, likely degrading and very likely degrading). For all water quality indicators, except MCI, more sites showed signs of improving rather than degrading trends over the last 10 years (Figure 1). However, there were many degrading sites for all indicators, which shows that more work is required to maintain or improve New Zealand’s waterways.
When looking at the ‘very likely’ trend categories, which give greater certainty that an improving or degrading trend is occurring, the water quality improvements were more common than degradations for all water quality parameters, except for MCI and DRP (Figure 1, Table 1). For example, water clarity has more than five times as many sites with improving trends than degrading trends, but for MCI more than double the number of sites showed trends that are ‘very likely degrading’ than ‘very likely improving’.
At some sites there is insufficient evidence to clearly say if water quality is improving or degrading – i.e. indeterminate trends. MCI has the highest proportion of indeterminate sites of all water quality indicators with one third of the sampled sites showing neither a clear improvement nor clear degradation over the last 10 years.
Figure 1. Summary of the proportion of sites with improving, indeterminate or degrading trends over the last 10 years (2008 - 2017). 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 be assessed for trend for each parameter is shown at the top of the bar.
Table 1. The number of sites showing different levels of confidence of improvement or degradation over the last 10 years (2008 – 2017) for nine water quality parameters (eight physiochemical water quality indicators and one biological water quality indicator). There was insufficient evidence to say whether water quality is 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.
LAWA has adopted a new trend analysis approach for October 2018. This new approach is considered the most accurate trend analysis methodology for the assessment of water quality to date. Detailed information on calculating water quality trends can be found on the ‘Calculating water quality trends’ factsheet.
1For more detailed information on this trend analysis see LAWA’s factsheet on calculating water quality trends
2Sites with suitable data were available from all regional and unitary council regions and from the National River Water Quality Network run by NIWA.