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Temperature data means monitoring thermal loading or discharge and determining changes in the thermocline that affect the health of aquatic species and organisms. Water temperature is a basic property, and many parameters depend on it for accuracy. The water temperature sensor housed in the Waka monitors temperature every 15 minutes.

What Affects Water Temperature?

Water temperature varies naturally with the seasons. Temperature determines how many animals and plants live in waterways. Water at the bottom of a waterway is typically colder due to groundwater input, while water on the surface is warmer due to higher air temperature.

Many different activities can change water temperatures, including discharging warmer water from thermal power stations, releasing water from dams, and alike. A reduction or increase in water level from diversion can also affect water temperature.

What Can Temperature Indicate About Water Quality?

The temperature has a significant influence on biological activity. It impacts the rate of chemical and biological reactions, as it affects the photosynthesis of aquatic plants, aquatic lifes’ metabolic rates and how sensitive such organisms are to pollution, parasites and disease.

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In addition, water temperature is crucial because of its influence on water chemistry. Chemical reactions tend to increase at higher temperatures. The temperature of the water can affect quality in various ways. When the temperature rises, water will hold more dissolved solids but fewer gases.

The Effects of Water Temperature Changes

Many animals and plants that live in our waterways prefer a certain temperature range. This is because growth and reproduction rely on specific temperatures. So when the temperature does change outside of the preferred range, it can significantly impact life in waterways.

While plants and algae that use photosynthesis prefer warm water where there is less dissolved oxygen, bacteria also tend to grow more rapidly in warm waters. Conversely, colder water contains more oxygen, which is better for animals like fish. Other effects of water temperature changes include:

  • Decreases in dissolved oxygen with increasing temperatures, which also reduces oxygen available for mahinga kai.
  • Increases in fish metabolic rate, as sudden changes, like changes at discharge points, can cause stress and lead to death.

  • Increases in nutrients like nitrates, so algal growth increases as the water gets warmer, resulting in algae blooms.

  • Changes in animals present, as some animals cannot tolerate significant temperature changes and will avoid such areas of waterways if unfavourable conditions.

How Does a Water Temperature Sensor Work?

Put simply, a water temperature sensor or probe tests the temperature of the water. So when chemical treatment is involved, rates of chemical reactions will decrease with decreasing temperature.

Related much to the pH value, when the water temperature is higher, it can multiply the bactericidal effectiveness of chlorine and its effectiveness in killing viruses. So at low temperatures, bacterial activity can significantly decrease.


The optimal temperatures for rainbow and brown trout are 16.5 - 17.2ºC and 10 - 15.5ºC. Dangerous temperatures are 25 - 26.6ºC and 23 - 26.4ºC.


Longfin and shortfin eels prefer water temperatures of around 22 - 25ºC but they can tolerate temperatures up to 34ºC.


The ideal temperature for salmon to thrive is between 4.5 - 10ºC. King salmon function best in temperatures between 12 - 17ºC.


The optimal temperatures for rainbow and brown trout are 16.5 - 17.2ºC and 10 - 15.5ºC. Dangerous temperatures are 25 - 26.6ºC and 23 - 26.4ºC.

What Does Temperature Monitoring Mean for Water Quality?

Water temperature changes affect many areas of life that rely on water, from aquatic life and ecosystems to primary industries. Much like how the effects of water temperature changes are discussed, water temperature monitoring means understanding what environment is required for different species.

Why Water Temperature is Important

Water temperature is one of the most important characteristics of an aquatic system. It affects Dissolved Oxygen levels, chemical processes, biological processes, water density and stratification, and environmental cues.

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Water Temperature Changes and Quality Updates

The RiverWatch blog is the data centre for New Zealanders committed to monitoring and enhancing our waterways. Learn more about the water quality of New Zealand and our integral connection with the waters, and stay up to date with important news, research and developments.