River water quality for ecological health

Why we monitor river water quality for ecological health

Photo of banded kopuku Waikato Regional Council routinely monitors a representative cross-section of regional rivers and streams to assess the suitability of water quality for native water plants and animals.

Sensitive aquatic plants and animals cannot live and thrive when water quality is poor.

Some contaminants (like ammonia and heavy metals) are toxic to aquatic organisms; others use up the dissolved oxygen that aquatic organisms need to breathe. Water that is too warm can stress sensitive fish and animals. Nuisance growths of water plants, algal slimes, and phytoplankton blooms can thrive when there are excessive levels of plant nutrients.

What's happening?

We monitor 115 sites on regional rivers and streams throughout the region. You can see more about those sites and their results, here.

An average ‘pass rate’ for seven water quality measures (dissolved oxygen, pH, turbidity, ammonia, temperature, nitrogen and phosphorus) is determined for each site by comparing sample results with national and local guidelines for ecological health.

Water quality for ecological health is good in some parts of the region (for example, Upper Waikato River, tributaries of Lake Taupō and in the Coromandel). In the lowland areas water quality is not so good (for example, Hauraki, lowland tributaries of the Waikato River).

This largely reflects the greater intensity of land use in the lowland parts of the region, with higher levels of nitrogen and phosphorus, and highlights the importance of non-point sources of contamination such as runoff from agricultural land and urban areas.

We can assess the relative importance of various point and non-point sources of contamination using information from this indicator and Waikato Regional Council's resource consents database.

Methods - How we monitor

Where and how we collect the data

We do routine monitoring of river water quality under two main programmes. This monitoring provides information on the condition of the water so that we can assess its suitability for desired uses (for example, supporting healthy ecosystems, human recreation). The programmes are:

Waikato River monitoring programme
Regional rivers monitoring programme (which covers rivers throughout the region, other than the Waikato River).

Monitoring sites

We have 10 sites on the Waikato River and 105 sites on other rivers and streams (including two NIWA sites).

Sites are grouped into two river reaches (upper and lower reaches of the Waikato River) and seven zones.

Table 1: Water quality monitoring river reaches and zones

River reaches and zones	Number of sites
Upper Waikato River	5
Lower Waikato River	5
Coromandel	11
Hauraki	13
Inflows to Lake Taupō	13
Upland tributaries of the Waikato River	12
Lowland tributaries of the Waikato River	26
Waipa River and tributaries	16
West Coast	14
Total	115

Monitoring frequency

Each site is visited at monthly intervals.

Monitoring history

The Waikato Regional Council began monitoring sites on the Waikato River between 1980 and 1987. The regional rivers programme started monitoring between 1993 and 1994.

Measurement technique

Water quality is measured by taking some measurements on site (for example, water temperature and water clarity) and taking samples of water back to the laboratory for analysis. More than 20 water quality variables are measured, including:

physical variables (for example, temperature, pH, turbidity)
chemical variables (for example, dissolved oxygen, arsenic, nitrogen and phosphorus)
microbiological variables (for example, faecal coliforms, Escherichia coli).

How this indicator is compiled

Three categories of water quality for ecological health were developed: excellent, satisfactory and unsatisfactory. These were based on ‘critical values’ for seven water quality variables we identified as relevant to the suitability of river water for ecological health:

dissolved oxygen
pH
turbidity
ammonia
temperature
total phosphorus
total nitrogen.

Check out the table below for critical values for the three categories that were derived from national or other standards and guidelines, and from expert opinion.

At each monitoring site, the proportions of all samples collected during 2015-2019 for a given water quality variable which met the standard for excellent water quality were determined. Similarly the proportions which met the standard for satisfactory and unsatisfactory water quality were determined. This process was undertaken for all seven variables.

At each site, the average value of the proportions found to be ‘excellent’ for each of the seven variables was calculated. Average proportions for the ‘satisfactory’ and ‘unsatisfactory’ categories were also calculated.

The results for the individual sites were then aggregated according to site location. Results from the Waikato River sites upstream of Lake Karapiro were aggregated into an ‘Upper River’ result, while the other sites were aggregated into a ‘Lower River’ result. The results for the other sites were aggregated into seven ‘water zones’.

Guidelines and standards

The table below lists the water quality guidelines and standards used.

Table 2: Guidelines and standards used to assess water quality for ecological health

Water quality variable (units)	Relevance		Categories
		Excellent	Satisfactory	Unsatisfactory
Dissolved oxygen (% of saturation)	Oxygen for aquatic animals to breathe	>90	80–90	<80
pH (acidity)	Can affect plants and fish	7–8	6.5–7 or 8–9	<6.5 or >9
Turbidity (NTU)	Can restrict plant growth	<2	2–5	>5
Ammonia (g N/m³)	Toxic to fish	<0.1	0.1–0.88	>0.88
Temperature (°C)	Fish spawning May-Sep	<10	10–12	>12
	Fish health Oct-Apr	<16	16–20	>20
Total phosphorus (g/m³)	Causes nuisance plant growth	<0.01	0.01–0.04	>0.04
Total nitrogen (g/m³)	Causes nuisance plant growth	<0.1	0.1–0.5	>0.5

The aggregation of river water quality data within a zone or reach ignores any differences between the sites in a given zone or reach.
Quality control procedures
Tulagi, A. 2017. Waikato River Water Quality Monitoring Programme: Data Report 2016. Waikato Regional Council Technical Report 2017/14. Waikato Regional Council, Hamilton.

Results - data and trends

The Excel spreadsheet below contains the source data for this indicator's graph and information.

The graph shows the percent of samples from rivers around the region that met or exceeded our guidelines for excellent, satisfactory or unsatisfactory water quality for ecological health.

You can also see the individual monitoring results at each our monitored sites, here.

The data were collected from 2015-2019.

Percentage of samples meeting our guidelines for excellent, satisfactory or unsatisfactory river water quality for ecological health (2015-2019)

Graph for river water quality for ecological health (2015-2019)