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Estuarine water quality report

Why we monitor estuarine water quality

Sensitive aquatic plants and animals cannot live and thrive when estuarine water quality is poor.  Some contaminants (like ammonia) are toxic to aquatic organisms; others use up the dissolved oxygen that aquatic organisms need to breathe.  Nuisance and harmful algal blooms can thrive when there are excessive levels of plant nutrients. 

Poor water quality can also limit people’s enjoyment of coastal waters for contact recreation or shellfish-gathering.  Some micro-organisms found in faeces or dung can make people sick if they are present in high levels in water used for contact recreation or shellfish-gathering.  When feeding, shellfish can filter large volumes of seawater, so any contaminants present in the water become concentrated in the shellfish flesh.  This means the water quality needs to be better for shellfish-gathering than for contact recreation.

This indicator shows how suitable our estuarine water quality is (1) for aquatic plants and animals to live there (“ecological health”), (2) for contact recreation, and (3) for shellfish-gathering. 

The ecological health part is based on the average “pass rate” for seven water quality measures:

  • dissolved oxygen
  • pH
  • turbidity
  • total ammonia
  • nitrate
  • phosphorus
  • algal biomass (chlorophyll a)

The contact recreation part is based on the average “pass rate” for a single water quality measure:
enterococci bacteria – single sample.

The shellfish-gathering part is based on the average “pass rate” for two water quality measures:

  • faecal coliform bacteria – median
  • faecal coliform bacteria – 90 percentile

What's happening?

Water quality for ecological health in the region’s estuaries is generally satisfactory or better.  Water quality for contact recreation is often excellent.  But water quality for shellfish-gathering can be unsatisfactory at times, particularly after heavy rain, due to increased contaminated runoff from the land.

Waikato Regional Council operates a modest estuarine water quality monitoring programme, and has thus far sampled conditions in seven estuaries in the region.  View a map showing the location of the seven estuaries. 

An average “pass rate” for seven measures of water quality for ecological health (dissolved oxygen, pH, turbidity, total ammonia, nitrate, total phosphorus and chlorophyll a) is determined by comparing results with national and local guidelines.  Similarly, “pass rates” are determined for measures of water quality for contact recreation (enterococci) and for shellfish-gathering (faecal coliforms). 

>> Find out more about these data and trends

More information

When this indicator is updated

This indicator is updated following the completion of each new estuarine survey. During 2013-14 an eighth estuary was also studied, and one of the original set was re-surveyed. 

Contact at Waikato Regional Council

Water Quality Scientist - Science and Strategy Directorate