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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 Summary 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 River Water Quality National Picture Summary 2020

27 September 2020

LAWA shows water quality information for river sites throughout New Zealand. Rivers and streams are monitored for a range of water quality (chemical-physical and bacterial) and ecological indicators by regional and unitary councils, and the National Institute of Water and Atmospheric Research (NIWA). Water quality information is now available from 1500 river sites, up from 1100 sites six years ago when LAWA was initiated.  State and trends for these indicators have been updated for data up to the end of December 2019.

In this national picture summary, LAWA is focusing on the state of our rivers and streams, how it compares among different land cover types and how it has changed over time. Here we report on: 1) a biological indicator of ecosystem health (macroinvertebrate community index - MCI), 2) an indicator of safety of water for human contact (E. coli), 3) a nutrient that can be toxic to instream life (ammonia toxicity), and 4) a key nutrient (dissolved reactive phosphorus - DRP) which can lead to problematic algal growth.

This summary provides some information on how water quality and stream health in New Zealand are tracking overall. However, it is important to note that this information only relates to sites where monitoring has been conducted. Monitored sites are often located in areas at greater risk from human activities, so these sites are not necessarily fully representative of all our rivers and streams.

In the future, we hope to further align our reporting with the recently released National Policy Statement for Freshwater Management 2020 (Freshwater NPS 2020) and include information from a wider variety of attributes when data becomes available over time.

 

Current state by land cover

LAWA evaluates conditions at sites nationwide against the National Objectives Framework (NOF) described in the Freshwater NPS 2020, where expectations of each indicator’s values are defined as achievement bands, from A (good) to D or E (poor). This evaluation requires an almost complete history of monthly measurements over the previous five years before a grade can be assigned, so not all sites that feature on the LAWA website can be graded. The ‘current state’ for 2019 at each site is based on data over the last five years (from 2015 to 2019).

Land use is a key driver of water quality and ecosystem health. In the following analyses we show differences in current state for 2019, among four different land cover categories, as defined by the River Environment Classification (REC) system. There is a consistent pattern among land cover categories for all four indicators that we are focusing on in this national summary (Figures 1-4) – with the highest proportion of better scoring streams in native vegetation, followed by exotic forest and then pasture. Urban streams generally receive the worst scores.

Rivers and streams with catchments classified as being predominantly native vegetation make up 48% of Aotearoa New Zealand’s channel length, while pasture is also common making up 45%. Exotic forestry streams (5% of channel length) and urban streams (1%) are less common. So, while urban streams generally have the worst instream health, they are relatively uncommon throughout Aotearoa New Zealand.

Although catchments in the native vegetation land cover class are the least affected by our activities, they are not fully representative of natural conditions because, their definition allows them to include some urban, pasture, and exotic forest land cover in the catchment upstream, if they are still predominantly in native vegetation. This might explain why some “native vegetation” sites are in the D band. Geological differences among streams may also explain high concentrations for some parameters. For example, phosphorus concentrations tend to be naturally high in catchments draining volcanic soils. 

 

LAWA National River Water Quality State (2019) by Land Cover Class

Macroinvertebrate Community Index (MCI)

Figure 1. Comparison of NOF bands for the macroinvertebrate community index (MCI) across four land cover classes. Bands were calculated from median MCI scores over the 5-year period from 2015-2019 at 995 sites. The number of sites with suitable data to determine the NOF band for each land cover class is shown at the bottom of each bar. The location of these monitoring sites is shown on the map.

 

LAWA National River Water Quality State (2019) by Land Cover Class

E. coli

Figure 2. Comparison of NOF bands for the faecal indicator bacteria E. coli across four different land cover classes. Bands were calculated over the 5-year period from 2015-2019 at 757 sites. The number of sites with suitable data to determine the NOF band for each land cover class is shown at the bottom of each bar. The location of these monitoring sites is shown on the map.

 

LAWA National River Water Quality State (2019) by Land Cover Class

Ammonia Toxicity

Figure 3. Comparison of NOF bands for ammonia toxicity across four different land cover classes. Bands were calculated over the 5-year period from 2015-2019 at 678 sites. The number of sites with suitable data to determine the NOF band for each land cover class is shown at the bottom of each bar. The location of these monitoring sites is shown on the map.

 

LAWA National River Water Quality State (2019) by Land Cover Class

Dissolved Reactive Phosphorus (DRP)

Figure 4. Comparison of NOF bands for dissolved reactive phosphorus (DRP) across four different land cover classes. Bands were calculated over the 5-year period from 2015-2019 at 788 sites. The number of sites with suitable data to determine the NOF band for each land cover class is shown at the bottom of each bar. The location of these monitoring sites is shown on the map.

 

How state has changed over time

The above plots look at the current state, but how has this state changed over time? To examine this, we looked only at sites that had an almost complete sampling record over the last 15 years. This enabled us to calculate state bands for each year over the last decade. Each state assessment is based on the previous five years of information, so the 2010 grades, for example, are based on a five-year dataset from 2006-2010. The following plots show results only for those sites that have this long and comprehensive sampling history.

 

Macroinvertebrate Community Index

Macroinvertebrates are small insects, worms and crustaceans that live on or just below the stream-bed. They are sampled to provide an indicator of the ecological health of wadeable streams and rivers. Species that are sensitive to poor water quality are only found at healthy sites whereas species that are tolerant of poor water quality tend to dominate the macroinvertebrate community at polluted sites. The MCI score summarises the pollution tolerances of the species that make up the community at a site.  The proportion of sites in each band appears to be relatively consistent over the last ten years (Figure 5). Ideally, we would have liked to see a reduction in the number of sites in the D and C bands, but there is no evidence for this. 

 

LAWA National River Water Quality State Change Over Time (2010 - 2019)

Macroinvertebrate Community Index (MCI)

Figure 5. Changes in NOF band for the macroinvertebrate community index from 2010-2019 at the 457 sites where there were enough data to determine a result each year.

 

Faecal indicator bacteria

E. coli is the main type of faecal indicator bacteria monitored in freshwater systems. High concentrations of E. coli indicate that there are significant sources of faecal matter upstream – such as stock inputs, surface water runoff, or untreated wastewater discharges. High levels of indicator bacteria in the water are a concern as they suggest other harmful bacteria or pathogens may be in the water which can make us sick.

Faecal indicator monitoring is done at popular swimming sites during the summer as well as year-round at State of the Environment monitoring sites. The data presented here are from the State of the Environment sites only and show that more than half of the sites are scoring poorly, and are in the D and E bands. There is no evidence of a reduction in the number of sites in these bands over the last 10 years (Figure 6).

 

LAWA National River Water Quality State Change Over Time (2010 - 2019) 

E. coli

Figure 6. Changes in NOF band for the faecal indicator bacteria E. coli from 2010-2019 at the 220 sites where there were enough data to determine a result each year.

 

Ammonia toxicity

Ammoniacal nitrogen can be a problem downstream of wastewater discharges or intensive farming. The assessment grades applied to ammonia concentrations defined in the NOF apply only to its potential toxicity on instream fauna. Ammonia is also a nutrient that may potentially contribute to the excessive growth of algae and other aquatic plants. Ammonia levels must be quite high before it results in poor ammonia toxicity grades. Sites assessed as having A and B bands for instream toxicity effects can still have ammonia levels that increase the risk of excessive algal growth. Most monitoring sites had levels of ammoniacal nitrogen that were below levels where toxicity is likely. This has been a consistent picture over the last 10 years (Figure 7).

 

LAWA National River Water Quality State Change Over Time (2010 - 2019)

Ammonia Toxicity

Figure 7. Changes in NOF band for ammonia toxicity from 2010-2019 at the 238 sites where there were enough data to determine a result each year. 

 

Dissolved reactive phosphorus

Phosphorus is an important nutrient contributing to the growth of algae and other aquatic plants in freshwater systems, but when phosphorus concentrations are high there is an increased risk of nuisance algal blooms occurring. We often focus on dissolved reactive phosphorus because that is the phosphorus component that is most available for uptake by aquatic plants. Dissolved reactive phosphorus results have been largely stable over time, perhaps with some indication of a reducing number of sites in the D-band (Figure 8).

 

LAWA National River Water Quality State Change Over Time (2010 - 2019)

Dissolved Reactive Phosphorus (DRP)

Figure 8. Changes in NOF band for dissolved reactive phosphorus from 2010-2019 at the 318 sites where there were enough data to determine a result each year.