River water quality for contact recreation

Methods - how we monitor

• Where and how we collect the data

  We carry out routine monitoring of river water quality under two main programmes:

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

  This monitoring provides information on the condition of the water so that we can assess its suitability for uses (such as supporting healthy ecosystems or human recreation).

  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 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. Monitoring started at the two NIWA regional rivers sites between 1989 and 1990.

  Measurement technique

  We measure water quality by either taking measurements on site (for example, water temperature and water clarity) or taking samples of water back to the laboratory for analysis. We measure more than 20 water quality variables. They include:

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

  Only the water clarity and microbiological data are used for this indicator.
• How this indicator is compiled

  The Waikato Regional Council has developed three categories of river water quality for contact recreation:

  1. excellent
  2. satisfactory
  3. unsatisfactory.

  We based these categories on the ‘critical values’ for two water quality variables that are relevant to the suitability of river water for contact recreation. The variables are:

  1. water clarity at baseflow
  2. Escherichia coli – 95th percentile.

  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, we determined the proportions of all samples collected during 2015-2019 for a given water quality variable which met the standard for excellent water quality. Similarly, we determined the proportions that met the standard for satisfactory and unsatisfactory water quality. This process was undertaken for both variables.

  At each site, we calculated the average value of the proportions found to be ‘excellent’ for both of the variables. We also calculated the average proportions for the ‘satisfactory’ and ‘unsatisfactory’ categories.

  We then aggregated the results for the individual sites according to site location. We also aggregated the results from the five Waikato River sites upstream of Lake Kāarapiro into an upper river result, and the other sites into a lower river result. The results for the other 105 sites were aggregated into seven water zones.

  Guidelines and standards

  The table below lists the river water quality guidelines used.

  Table 2: Guidelines used to assess river water quality for contact recreation

  Water quality variable (units)	Relevance		Categories
  		Excellent	Satisfactory	Unsatisfactory
  Clarity, baseflow (m)	Visibility	>4	1.6 – 4	<1.6
  Escherichia coli, 95th percentile	Human health	<55	55 – 550	>550

  Notes

  1. ‘Baseflow’ is defined as flows less than the upper decile flow (noting that people are less likely to want to swim when river flows are high).
  2. The 95th percentile value of E. coli in the 2003 national guidelines is 550 units per 100 mL. We use this value to define unsatisfactory conditions.
  3. 'Excellent' conditions have an E. coli level one-tenth of the 'action' value (55 units per 100 mL).
• Limitations
  • The aggregation of river water quality data within a zone ignores any differences between the sites in that zone.
  • Levels of faecal bacteria in rivers are known to vary markedly with time, so the three-monthly sampling probably provides only a broad indication of ‘typical’ levels.

  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.