Bacterial monitoring

The Environmental Health Directorate in partnership with local government test a number of popular Western Australian swimming beaches for bacteria. These include the:

• Swan and Canning Rivers
• Perth metropolitan coastal beaches and
• Rottnest Island.

Why monitor?

We monitor the bacterial water quality so we can:

• Make sure the water is safe to swim in.
• Classify water bodies to help you decide where you want to swim.
• Issue warnings during pollution events.
• Identify bacterial pollution sources.
• Look for long-term bacterial trends.

When are waters monitored?

In general, recreational waterways are monitored once every fortnight from November to April when people usually go swimming.

Monitoring during winter is not considered necessary as majority of the public do not go swimming during these times.

What do we test for?

Samples are tested in a laboratory for a group of bacteria called enterococci. Enterococci are commonly found in the gut of warm blooded animals and humans. High levels of these bacteria can help indicate a decrease in water quality for swimmers. Although enterococci are not harmful themselves, they can indicate the possible presence of harmful microorganisms such as bacteria, viruses and protozoa.

What are the results of sampling compared to?

In October 2005 the National Health and Medical Research Council released the Guidelines for Managing Risks in Recreational Water. These guidelines use a new approach to manage recreational water issues by looking at the bacteria levels in the water as well as everything else in and around the water such as stormwater drains, septic tanks and animals that may play a role in decreasing the bacterial water quality.

All this information is combined to assign a beach grade to the water so you as a water user can have a better understanding of the water quality and make a more informed decision about where and when you would like to go swimming.

What do the beach grades mean?

There are five beach grades – Very good, good, fair, poor or very poor – which have been placed into three different colours, green, amber or red. Green represents the safer areas to swim, whilst red represents the areas of higher risk. The grades are defined below:

	Very Good: Water is considered satisfactory for swimming at all times. Consistently very good water quality tests and very few potential pollutant sources identified at this beach indicate that water quality at this location should be of a high standard. Good: Conditions are safe for swimming most of the time. Water quality tests are generally good on nearly all occasions and there are few potential pollution sources identified. Standard advisories should be followed such as avoiding swimming for up to 3 days after heavy rainfall (e.g. >10mm) in river and estuarine waters due to the possible presence of stormwater contamination.
	Fair: Conditions are generally okay for swimming, although water quality tests may show times of elevated bacteria mostly due to animal pollutant sources (e.g. bird faeces) and rainfall. Swimming should be avoided during and subsequent days following heavy rainfall (e.g. >10mm), and if the water is discoloured.
	Poor: Conditions may not always be okay for swimming, as indicated by past results. The water can be affected by elevated bacteria, mostly during and following rainfall events, or due to animal pollutant sources (e.g. bird faeces). There may be a higher risk of illness if you ingest the water during these times, particularly by the very young, the very old and those with compromised immunity. Swimming or putting your head under the water should be avoided during these times. Other factors such as low dilution, tidal movement, wind direction and stormwater pollution may help pathogens survive longer in these waters. Swimming should be avoided during and subsequent days following heavy rainfall (e.g. >10mm), and if the water is discoloured. Activities such as canoeing, boating and fishing are still suitable. Very Poor: Avoid swimming at these locations, as there are direct discharges of faecal material. Permanent signage may be erected at the beach stating that swimming is not recommended.

How often are beach grades assigned?

Beach grades are assigned each year as we start to get a better understanding of the bacterial water quality at our beaches. At the moment all grades are temporary because they are based on limited bacterial data. This means the temporary grades may be deliberately conservative and categorise the water into a higher risk classification.

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