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Water quality

What is water quality?

Water quality is a key environmental asset in Port Phillip Bay, the Yarra River and associated waterways. Good water quality is vital to provide:
  • healthy and diverse ecosystems
  • clean, safe swimming 
  • recreational and commercial fishing and aquaculture industries.
When thinking about water quality, it’s good to remember that the needs of the animals and plants that live in the water aren’t always the same as the needs of humans who use the water. For example, conditions that may not be suitable for people to swim in (like high numbers of bacteria in the water) may not impact fish or other animals at all. For this reason water quality is referred to as either recreational or environmental.

What is our water quality like?

Overall, water quality in Port Phillip Bay and local waterways compare well to similar rivers and bays in urban areas overseas. Port Phillip Bay generally has both good environmental and recreational water quality. However, issues such as stormwater and algal blooms still can impact the bay, making it vital we continue to carefully monitor and manage this important asset.

Water quality in the Yarra has improved significantly over the past few decades, but does still vary along its length both in terms of environmental and recreational water quality. High environmental and recreational water quality is seen in the upper catchment, where the river flows through protected forests. As the river moves into more rural and urbanised areas, the environmental water quality decreases. In these sections of the catchment, higher volumes of rural and stormwater runoff can carry pollutants into waterways. 

Recreational water quality throughout the Yarra is generally suitable for boating and similar activities, while the less urbanised areas higher in the catchment are more likely to be suitable for swimming.

Other rivers around the bay will generally follow a similar water quality trend – higher quality in forested areas and lower quality in urban settings.

What are the measures of recreational water quality?

Recreational water quality is assessed from a human health perspective. 

All waterways contain micro-organisms such as algae, bacteria and parasites. The type and number of micro-organisms will determine if a water-body meets the recreational water quality standards for human needs.

Recreational water quality standards vary with the type of recreation – either primary (swimming) or secondary (boating) contact – with stronger standards required for primary contact where a high degree of bodily contact with the water, immersion and ingestion are likely. 

Water contaminated with faecal material may pose a risk of infection to swimmers and those undertaking contact water sports.
Assessment of recreational water quality is typically based on the use of two bacterial indicators of faecal contamination, E. coli and enterococci. 

What are the measures of environmental water quality?


Nitrogen and phosphorus are essential nutrients for plant and animal growth. Excessive levels of nutrients can greatly impact aquatic plants and subsequently environmental water quality, by promoting the growth of organisms like blue-green algae. 


Turbidity is a measure of water clarity (how clear the water is). High turbidity (low clarity) is caused mainly by large concentrations of sediments that are washed off catchments into streams and rivers, and ultimately into the bay. High levels of sediments can significantly impact the health of aquatic ecosystems. 


Metals occurring naturally in the earth's crust are released into the environment from the physical and chemical weathering of rocks. However, metals produced by humans are found in industrial and municipal waste products, urban and agricultural runoff, atmospheric deposition and antifouling paints applied to marine vessels. Most metals are toxic to organisms above certain levels.


Salinity refers to how much salt is in the water. The water in rivers and streams is usually fresh, oceans are salty and estuaries are highly variable depending on tides and freshwater flows. Most aquatic organisms have evolved to function within an optimal salinity range and tolerate natural cycles within this range.

Dissolved Oxygen

Dissolved oxygen (DO) refers to the amount of oxygen contained in water. Most aquatic animals and plants need oxygen to be above a certain level, and this level can vary depending on the organism. Either too little or too much oxygen in the water can have negative impacts on their physical wellbeing.


pH is a measure of acidity or alkalinity of water ranging from acidic (pH less than 7) through to neutral (pH 7) and alkaline (pH greater than 7). Most aquatic organisms require pH to be within a particular range. If pH is outside this range, the effects can be detrimental to aquatic animals and plants. 


Chlorophyll-A is a green pigment found in plants. It absorbs sunlight and converts it to sugar during photosynthesis. Concentrations of chlorophyll-a are measured in the water to assess the level of algae. Higher concentrations can indicate poorer environmental water quality.

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