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Dissolved Oxygen

Dissolved oxygen indicates an aquatic resource’s ability to support aquatic life. Colder water can hold more oxygen, and warmer water can hold less oxygen. Low dissolved oxygen levels threaten fish and aquatic organisms’ survival.

Is Dissolved Oxygen in Water Good or Bad?

Adequate dissolved oxygen is necessary for good water quality. As oxygen is a necessary element for all forms of life, other processes, like natural stream purification, require adequate oxygen levels to provide for aerobic life forms.

What is a Healthy Level of Dissolved Oxygen in Water?

6.5-8 mg/L

Water at lower temperatures should have higher mg/L of dissolved oxygen. However, polluted waters will likely have lower mg/L. Healthy water should usually have dissolved oxygen concentrations above 6.5-8 mg/L.

Conductivity Water Quality Sensor Monitor

If dissolved oxygen levels drop below 5.0 mg/L, it puts aquatic life under stress. Therefore, the lower the concentration, the greater the stress. If oxygen levels remain below 1-2 mg/L for a few hours, it can result in many fish deaths.

Factors That Change Dissolved Oxygen Levels

Temperature impacts dissolved oxygen levels. So, for example, colder water can hold more oxygen, while warmer water can hold less oxygen.

Dissolved oxygen levels can also increase due to wind and wave action, adding plants to the water body and exposing the water to purified oxygen.

Low dissolved oxygen can result from excessive algae growth caused by excess nutrients like nitrates and phosphorus. In addition, as algae die and decompose, this also contributes to decreased dissolved oxygen levels.

Dissolved Oxygen Sensor

How Does Dissolved Oxygen Indicate Water Quality

When dissolved oxygen becomes too low, fish and other aquatic life cannot survive. All aquatic animals need dissolved oxygen to breathe. Low levels of oxygen (hypoxia) or even no oxygen levels (anoxia) equals poor water quality.


Why Are Dissolved Oxygen Sensors Important?

Oxygen is necessary for many aquatic species to survive. Dissolved oxygen sensors indicate how much oxygen is dissolved in water for fish to breathe. Healthy water bodies have high levels of dissolved oxygen in the water. Organic debris, including fallen leaves and sewage leaks, can cause dissolved oxygen concentrations to decrease.

Aquatic Life

Oxygen gets into the water in several ways and helps keep aquatic life alive. As oxygen from the atmosphere dissolves and mixes into the water’s surface, algae and underwater grasses also release oxygen during photosynthesis. As waters flow from and between streams, rivers, and oceans, a consistent flow of dissolved oxygen makes way to aquatic plants and organisms.

Natural Stream Purification

Self-purification of natural waterways occurs when sewage is discharged into them. The organic matter gets oxidised by bacteria and converted to stable substances. This process of oxidation requires the dissolved oxygen content of the waterway to be utilised. Water being polluted can be due to low dissolved oxygen levels and indicates poor water quality.

Aquatic Life

Oxygen gets into the water in several ways and helps keep aquatic life alive. As oxygen from the atmosphere dissolves and mixes into the water’s surface, algae and underwater grasses also release oxygen during photosynthesis. As waters flow from and between streams, rivers, and oceans, a consistent flow of dissolved oxygen makes way to aquatic plants and organisms.

Using Dissolved Oxygen Measurements to Monitor Water Quality

When levels drop, sensitive animals and aquatic life can move away, decline in health, and die, impacting New Zealand ecosystems and increasing the threat of native fish and species extensions and plants.

New Zealand Environmental Water Quality Monitoring with Real Time Io T Artificial Intelligence Water Monitor RW

Dissolved Oxygen and Water Monitoring 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.