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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
  • Clarity
  • Dissolved Reactive Phosphorus
  • Ammonia (toxicity)
  • Nitrate (toxicity)
  • Macroinvertebrate Community Index

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LAWA River Water Quality National Picture Summary 2021

Publish date: 26 September 2021

 

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 councils and unitary authorities, and the National Institute of Water and Atmospheric Research (NIWA). Data and information is now available from more than 1500 river sites, up from 1100 sites seven years ago when LAWA was initiated.  State and trends for these indicators have been updated using data up to the end of December 2020.

This national picture summary focuses on the state of our rivers and streams. Here we report on: 

1) A biological indicator of ecosystem health (Macroinvertebrate Community Index - MCI)

2) An indicator bacterium that can indicate faecal contamination and the presence of harmful pathogens which may cause illness to recreational water users (E. coli)

3) Nutrients that can be toxic to in-stream life (ammonia and nitrate toxicity)

4) A key nutrient that can lead to problematic in-stream algal growth (dissolved reactive phosphorus - DRP)

5) Suspended fine sediment that can affect the ecosystem health and amenity value of waterways (clarity)

This summary provides information on the state of river health in New Zealand, how it varies by land cover, and how it has changed over time. As data are only available for sites where monitoring has been conducted, and monitoring sites are often located in areas at greater risk of degradation from human activities, this summary is not necessarily a balanced representation of all rivers and streams across the country.

LAWA evaluates conditions (state) at sites nationwide against attribute bands described in the National Policy for Freshwater Management 2020 (NPS-FM 2020), from A (good) to D or E (poor). The 'current state' for 2020 at each site is based on monthly data over the last five years (from 2016 to 2020).  This evaluation requires an almost complete five-year history of monthly measurements before a grade can be assigned, so not all sites that feature on the LAWA website can be assigned attribute bands.

 

Current state by indicator

The current state of our rivers and streams varies by indicator (Figure 1).

Impaired ecological health is evident at almost two-thirds of monitored river sites, demonstrated by the proportion of MCI sites classified as attribute C and D.

New Zealand's primary indicator of faecal bacterial contamination (E. coli) shows a similar pattern, with two-thirds of monitored sites graded band D or worse.

Dissolved reactive phosphorus (DRP) and clarity are factors that contribute to river and stream ecosystem health. While it is positive that almost half of the sites assessed for clarity are in the A band, clarity at around two-fifths of sites is in the C and D bands indicating that suspended fine sediment is impacting these sites.

For DRP, which is a nutrient that may contribute to excessive in-stream plant growth, just over half of sites monitored are classified as attribute band C or D.

The toxic effects of nitrate and ammonia on aquatic ecosystems are an issue at only a small percentage of monitored sites.  Therefore, it is not likely that such toxicity is driving the widespread ecological health impairments we're seeing through the MCI results. It is important to note that nitrogen can also stimulate problematic plant and algae growth at lower concentrations than those causing direct toxic effects. When assessing risk of nutrients driving problematic plant and algae growth, resource managers often look at the combination of multiple forms of nitrogen, including the dissolved nitrogen (collectively referred to as dissolved inorganic nitrogen, or DIN). There are currently no attribute band definitions for DIN in the NPS-FM 2020, and therefore it is not included in the national picture summary.  The NPS-FM 2020 requires management of nutrients to protect the ecological health of waterbodies and we intend to report further on this as more data and reporting guidance become available.

 

LAWA National River Water Quality Summary of State (2020)

Figure 1. Percentages of monitored sites by attribute bands for all six indicators discussed in this national picture summary.  Bands were calculated over the five-year period from 2016-2020. The number of sites with suitable data to determine an attribute band for each indicator is shown below each bar. 

 

Current state by land cover

Land use is a key driver of water quality and ecosystem health. In the following analyses we show differences in state for 2020, among four different land cover categories, as defined by the River Environment Classification (REC) system. There is a general pattern among land cover categories for five of the six indicators that we are focusing on in this national summary (Figures 2-6) – 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 account for 5% of channel length and urban streams are less common at 1%. So, while urban streams generally have the worst in-stream health, they make up only a small proportion of total river length throughout Aotearoa New Zealand.

The catchments in the native vegetation land cover class, least affected by human activities, are not necessarily 100% naturally vegetated. The land cover definition allows them to include some urban, pasture, and exotic forest in the catchment upstream, as long as they are still predominantly in native vegetation. Geological differences (different rock types, high organic-content soils, remnant wetlands or peat) among streams may also explain high concentrations for some indicators. For example, phosphorus concentrations tend to be naturally high in catchments draining volcanic soils. Similarly, dissolved phosphorus and ammonia can be elevated in wetlands and high organic-content soils. The combination of these may explain why some “native vegetation” sites are not in the A band.

 

LAWA National River Water Quality State (2020) by Land Cover Class

Macroinvertebrate Community Index (MCI)

Figure 2. Comparison of attribute bands for the Macroinvertebrate Community Index (MCI) across four land cover classes. Bands were calculated over the five-year period from 2016-2020 at 995 sites. The number of sites with suitable data to determine an attribute band for each land cover class is shown below each bar. The location of these monitoring sites is shown on the map.

 

LAWA National River Water Quality State (2020) by Land Cover Class

E. coli

Figure 3. Comparison of attribute bands for the faecal indicator bacteria E. coli across four different land cover classes. Bands were calculated over the five-year period from 2016-2020 at 810 sites. The number of sites with suitable data to determine an attribute band for each land cover class is shown below each bar. The location of these monitoring sites is shown on the map.

 

LAWA National River Water Quality State (2020) by Land Cover Class

Ammonia (toxicity)

Figure 4. Comparison of attribute bands for ammonia (toxicity) across four different land cover classes. Bands were calculated over the five-year period from 2016-2020 at 789 sites. The number of sites with suitable data to determine an attribute band for each land cover class is shown below each bar. The location of these monitoring sites is shown on the map.

 

LAWA National River Water Quality State (2020) by Land Cover Class

Nitrate (toxicity)

Figure 5. Comparison of attribute bands for nitrate (toxicity) across four different land cover classes. Bands were calculated over the five-year period from 2016-2020 at 845 sites. The number of sites with suitable data to determine an attribute band for each land cover class is shown below each bar. The location of these monitoring sites is shown on the map.

 

LAWA National River Water Quality State (2020) by Land Cover Class

Dissolved Reactive Phosphorus (DRP)

Figure 6. Comparison of attribute bands for dissolved reactive phosphorus (DRP) across four different land cover classes. Bands were calculated over the five-year period from 2016-2020 at 845 sites. The number of sites with suitable data to determine an attribute band for each land cover class is shown below each bar. The location of these monitoring sites is shown on the map.

 

LAWA National River Water Quality State (2020) by Land Cover Class

Clarity (Suspended Fine Sediment)

Figure 7. Comparison of attribute bands for attribute bands for clarity (suspended fine sediment) across four different land cover classes. Bands were calculated over the five-year period from 2016-2020 at 510 sites and take into account the different suspended sediment classes defined in the NPS-FM 2020. The number of sites with suitable data to determine an attribute band for each land cover class is shown below each bar. The location of these monitoring sites is shown on the map.

 

River state over time

The above plots look at the current state, but how has state changed over time? To examine this, we identified sites that had an almost complete sampling record over the last 15 years. This enabled us to calculate attribute bands for each five-year interval over the last decade. Each state band assessment is based on the previous five years of information, so the 2011 grades, for example, are based on a five-year dataset from 2007-2011. The following figures show results only for those sites that have this long and comprehensive sampling history.

Macroinvertebrates 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 summarises the pollution tolerances of the species that make up the community at a river site. 

We would have liked to see a reduction in the number of sites in the C and D bands, but there is no evidence for this. Aggregated state for monitored sites is marginally worse over the past seven years with fewer sites in the A and B bands and more sites in the C and D bands (Figure 8).

 

LAWA National River Water Quality State Change Over Time (2011-2020)

Macroinvertebrate Community Index (MCI)

Figure 8. Changes in attribute bands for the Macroinvertebrate Community Index (MCI) from 2011-2020 at the 449 sites where there were enough data to determine a result each year.  The location of these monitoring sites is shown on the map.

 

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

E. coli monitoring is conducted 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 around two-thirds of these sites are scoring poorly and are in the D and E bands. There is no clear evidence of a reduction in the number of sites in these bands nationally, over the last 10 years (Figure 9).

 

LAWA National River Water Quality State Change Over Time (2011-2020) 

E. coli

Figure 9. Changes in attribute bands for the faecal indicator bacteria E. coli from 2011-2020 at the 275 sites where there were enough data to determine a result each year.  The location of these monitoring sites is shown on the map.

 

Ammonia is one of several forms of nitrogen that exist in aquatic environments. In addition to contributing to in-stream plant and algae biomass, at high concentrations ammonia is toxic to aquatic fauna. Most monitoring sites had levels of ammonia below where toxicity is likely. This has been a consistent picture over the last 10 years (Figure 10). 

 

LAWA National River Water Quality State Change Over Time (2011-2020)

Ammonia (toxicity)

Figure 10. Changes in attribute bands for ammonia (toxicity) from 2011-2020 at the 328 sites where there were enough data to determine a result each year.  The location of these monitoring sites is shown on the map.

 

In addition to contributing to in-stream plant and algae biomass, at high concentrations nitrate is toxic to aquatic fauna.  Sites assessed as having A and B bands for in-stream toxicity effects can still have nitrate levels that increase the risk of excessive algal growth, because this occurs at much lower concentrations than toxicity.  Most monitoring sites had levels of nitrate nitrogen that were below levels where toxicity is likely. This has been a consistent picture over the last 10 years (Figure 11).

 

LAWA National River Water Quality State Change Over Time (2011-2020)

Nitrate (toxicity)

Figure 11. Changes in attribute bands for nitrate (toxicity) from 2011-2020 at the 366 sites where there were enough data to determine a result each year.  The location of these monitoring sites is shown on the map.

 

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 (DRP) because that is the phosphorus component that is most available for uptake by aquatic plants. While DRP results have been largely stable over time, the number of monitored sites in the A and B bands have marginally improved over the past 10 years, with a corresponding drop in number of sites in the D band (Figure 12).

 

LAWA National River Water Quality State Change Over Time (2011-2020)

Dissolved Reactive Phosphorus (DRP)

Figure 12. Changes in attribute bands for dissolved reactive phosphorus from 2011-2020 at the 376 sites where there were enough data to determine a result each year.  The location of these monitoring sites is shown on the map.

 

The amount of fine sediment suspended in the water is a key factor affecting water clarity. High concentrations of suspended sediment can also affect the feeding behaviour of some aquatic organisms (they can’t see their food), affect their ability to breathe (it clogs up their gills), and can reduce the amenity value (it can be less pleasant for people to swim in discoloured water).  If sediment deposits on the stream bed it can influence habitat and food quantity/quality for aquatic life.  Suspended fine sediment also often carries phosphorus with it. Fine sediment can get into waterways via erosion and surface runoff from the land, erosion of stream banks, and from some discharges. Land use and management practices can have a big effect on erosion and run-off of fine sediment, but there are also natural differences in climate, geology, and slope which can influence sediment inputs to waterways. Therefore, the NPS-FM 2020 defines four different classes of stream based on their climate, geology and slope, which have different expectations in terms of water clarity. Sediment runoff is a significant issue affecting New Zealand’s freshwater bodies so it is promising to see some signs of improvement in water clarity in the 216 sites that have been monitored consistently over the last 15 years (Figure 13).

 

LAWA National River Water Quality State Change Over Time (2011-2020)

Clarity (Suspended Fine Sediment)

Figure 13. Changes in attribute bands for clarity (suspended fine sediment) from 2011-2020 at the 216 sites where there were enough data to determine a result each year. The attribute bands take into account the different suspended sediment classes defined in the NPS-FM 2020. The location of these monitoring sites is shown on the map.

 

This National Picture Summary provides an aggregated overview of the state of river and stream health across six indicators using data from regional councils, unitary authorities, and NIWA. As a project, we are working to align our reporting with the NPS-FM 2020 and include information from a wider variety of indicators as monitoring data becomes increasingly available over time. This year, individual river site pages have been upgraded to report available data for an increased number of water quality and ecological indicators. These new indicators include nitrate toxicity, suspended fine sediment (derived from visual clarity or turbidity data), and dissolved inorganic nitrogen (DIN).  Quantitative Macroinvertebrate Community Index (QMCI) and the Average Score Per Metric (ASPM) indicators will be added to LAWA in October.

Looking at individual site data alongside contextual information at a catchment and regional level is useful for community groups, landowners, and others interested in how local waterways are tracking. Information specific to monitored sites can be accessed either by clicking on a site dot on the map to the left of the LAWA main screen (desktop and tablet users), or by navigating menus to the region, then catchment, and then site of interest. The agency responsible for monitoring an individual site may be able to provide further contextual information on the results shown here.