Bacterial water quality


The Environmental Health Directorate, in partnership with many Local Government authorities, and some other stakeholders, collect water samples to test for bacteria, and assess the health of a number of popular waterways used for swimming, diving, surfing and skiing in WA.

The Site Status Overviews below detail the number of water samples that the Department of Health, Local Government authorities and other managing authorities will be collecting this swimming season. They also provide sanitary inspection activity updates to assess faecal pollution risks and provisional bacterial water quality classifications for each site.

For further information about provisional bacterial water quality classifications refer to Beach grade classification risks.

Why monitor?

Water is monitored for bacteria so we can:

  • make sure the water is safe to swim in and recreate
  • 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.

What are the sources of bacteria in water, and what are the potential health risks?

Bacteria in water can come from a number of sources including farming activities, domestic animals, human effluent and wildlife. Swimming and/or swallowing water contaminated with high levels of bacteria can put you at risk of illness such as gastroenteritis, skin irritations, or respiratory, ear and eye infections. This is why it is important to be aware of the common causes for high levels of bacteria in natural waterways so you can avoid swimming and other similar recreational activities during these times.

Which waterways are monitored?

Those popular recreational waterways which are monitored are located within the following local government jurisdictions or other commonly known areas within WA:

Perth Metropolitan Region





  • Swan and Canning River sites – LGA's & Department of Health

Regional WA






When are waters monitored?

In general, recreational waterways, south of the 28° latitude (~ Kalbarri) are monitored once every fortnight from November to May 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?


Water samples are tested in a laboratory for a group of bacteria called Enterococci. Enterococci are commonly found in the stomach 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.

Escherichia Coli

Some fresh to estuarine recreational waters e.g. lakes, rivers etc are also tested for another group of bacteria called Escherichia Coli (E.Coli). This group of bacteria is also commonly found in the stomach of warm blooded animals and humans and they are a very good indicator of faecal contamination in water, unfortunately this indicator bacteria group tends to die-off rapidly in increasingly saline waters and is therefore not a good indicator for ocean waters.


Some fresh water bodies are also tested for amoebae. A subset group of amoebae includes an organism ‘Naegleria fowleri’ which is responsible for the extremely rare but fatal disease amoebic menigoencephalitis (commonly referred to as amoebic meningitis). Read more about amoebic meningitis (Healthy WA).

What guidelines are sampling results compared against?

The National Health and Medical Research Council (NHMRC) (external site) 2008, Guidelines for Managing Risks in Recreational Water (NHMRC Guidelines) (external site) utilise the approach to managing recreational water by testing the bacteria levels in the water and identifying faecal contaminant sources in and around the water such as storm water drains, septic tanks and animals that may play a role in decreasing the bacterial water quality.

The bacterial water quality at a given site is assessed according to the 95th percentile of the numbers of Enterococci recorded at that site. The Department of Health has produced an easy-to-use template (The Enterotester) (Excel 288KB)  for calculating 95th percentile statistics for enterococci bacteria, standardised for comparison with the 95th percentiles used in the NHMRC Guidelines. ‘The Enterotester’ template is packaged together with step by step instructions (PDF 2.23MB) that have been developed to assist the user to work through this template.

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 bacterial water quality at a given site and make a more informed decision about where and when you would like to go swimming.

What do 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. Beach grades however, may be assigned as provisional or final classification depending on the amount of information that is available for a given site. For further information refer to Beach grade risk classifications.

How often are beach grades assigned?

Beach grades are re-assigned each year, following the primary swimming season. For the most part beach grades are provisional because they are based on limited bacterial data or incomplete site assessment information.

NOTE: Provisional grades are deliberately conservative, and they may over estimate the actual risk and categorise water quality into a higher risk classification levels.

For further information on bacterial water quality, please refer to specific beach grades for popular swimming and recreational locations throughout WA, or contact the Environmental Health Directorate on 9388 4999 or email

Relevant publications

Fact sheets

Forms and templates


More information

Environmental Health Directorate
Phone: 9222 2000
Produced by

Public Health