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  Environment » Natural Resources » Water » Rivers » How healthy are our rivers? » How we measure quality

How we measure quality

Photograph of staff sampling stream biology

Water quality is measured by either taking measurements on site or taking samples of water back to the laboratory for analysis.

How water quality is assessed depends on its use. Water suitable for some uses may be unacceptable for others. For example, water contaminated with treated sewage may be unsafe for swimming but still suitable for industrial cooling.

Aspects of water quality

The table below lists the different aspects of water quality we measure every month. It summarises why these are important and the guidelines used to assess them.

The water quality measures are divided into two groups:

  • ecological health - those measuring whether water quality is suitable for plants and animals living in a river

  • human use - those that measure whether water quality is suitable for human use and activities such as swimming. This is also called swimmability.

Our guidelines are based on national standards and guidelines.

Aspects of water quality monitored by Waikato Regional Council

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
Total 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
Human uses - recreation
Baseflow water clarity (m) Visibility >4 1.6 – 4 <1.6
Escherichia coli, single sample (no./100 mL) Human health <55 55 – 550 >550

 

How we assess stream health

Our staff have surveyed stream habitat and invertebrate communities (such as insects, crustaceans and worms) at more than 341 river and stream sites in the Waikato region since 1994. 

A wide variety of native and exotic fish, invertebrates, aquatic plants and algae are found in Waikato rivers and streams. The number and type of species found at each site provides an indication of stream health. Over 130 different types of invertebrates have been identified in Waikato Regional Council's ecological monitoring of streams programme.

Studies show that invertebrates differ in their tolerance to pollution and habitat quality. Habitat quality can vary naturally, for example through differences in channel gradient and streambed substrate size, as well as through people-induced factors such as clearance of riparian vegetation. Plants and animals living in the stream may also accumulate contaminants over time. Even though present at a contaminated site, they may not be as healthy as the same species living in less stressful conditions.

The types of invertebrates that are present in a sample enable us to calculate biological indicators that reflect overall stream health.

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