Microbial water quality

The Department of Health oversees microbial water quality monitoring of recreational/ environmental waterways in Western Australia, with water samples collected by many local government authorities and some other stakeholders. Water is tested primarily for bacteria and in fresh to brackish waters amoeba, to assess the health of popular waterways used for swimming, diving, surfing, skiing, wading, kayaking, fishing and boating etc.


The Department of Health, assess long-term bacterial water quality results and assign temporary beach grades to these popular recreational and other environmental water locations in accordance with the National Health and Medical Research Council, 2008, Guidelines for Managing Risks in Recreational Water (external site)

The Department of Health produces an annual site status overview for specific recreation / environmental water areas/ sites, which provides this beach grade, indicates the recommended minimum number of microbial water samples for collection during the upcoming swimming/ recreational season/financial year, and also summarises key sanitary inspection actions to assess and confirm faecal pollution risks for each site.

For further information about provisional bacterial water quality classifications, beach grades, or Site Status Overview’s see: Beach grade risk classifications and Beach grades for Western Australia.

Water is monitored for bacteria to:

  • 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.

Bacteria in water sources and potential health risks

Bacteria in water can come from several 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 or skin, respiratory, ear and eye irritations and/or infections. Therefore, it is important to be aware of common causes for high levels of bacteria in natural waterways so you can avoid swimming and other similar recreational activities during these times.

Waterways monitored

To see which popular recreational waterways which are monitored within WA, refer to the publications below and Beach grades for Western Australia.

Perth metropolitan region


Regional WA


When waters are monitored

For the Perth metropolitan, Peel, South West, Great Southern, Goldfields-Esperance, Wheatbelt regions, and the Mid-West and Gascoyne region areas south of the -26° latitude, the microbial water quality monitoring season extends between November to May for recreational/ environmental waters. Monitoring during the cooler/winter months is not considered necessary as majority of the public do not go swimming during these times.

For locations north of the -26° latitude (including the Kimberley, Pilbara and Gascoyne regions), microbial water quality monitoring can be undertaken at any time due to continued warm to hot weather but may be undertaken more regularly between May and November to cater for the peak tourist recreational water use season.

About testing

Microbes included in testing


Water samples are tested in a laboratory for a group of bacteria called EnterococciEnterococci 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, E. coli tend to die-off rapidly in increasingly saline waters and are therefore not a good indicator for marine 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).

Water sampling guidelines 

The National Health and Medical Research Council (NHMRC) (external site) 2008, Guidelines for Managing Risks in Recreational Water (NHMRC Guidelines) (external site) approach to managing recreational water quality is to test bacteria levels in the water, and to identify and risk-assess faecal contaminant sources in and around the water, such as storm water drains, septic tanks and animals that may impact 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. WA 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.

These water sample results (microbial assessment category) and the faecal risk-assessment (sanitary assessment category) combine to assign a beach grade, so that the water user can have confidence in the bacterial water quality and potential sources of faecal contamination for a recreational site and make a better decision about where and when they go swimming or undertake other recreational water activities.

About beach grades

Beach grades classifications

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.

Beach grading frequency

Beach grades are re-assigned each year following the primary swimming season. Beach grades are mostly provisional because they are based on limited bacterial data or incomplete sanitary assessment informationProvisional beach grades are deliberately conservative, due to gaps in available information, and hence may overstate the actual risk and categorise water quality into a higher risk level e.g. moderate or high.

Relevant publications

For relevant and supporting publications visit Environmental waters publications.

More information

Environmental Health Directorate
Phone: 9222 2000
Produced by

Public Health