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Delivering a Healthy WA
Healthy Swimming in Western Australian Waterways


Sewage overflows

Sometimes mechanical faults at sewage treatment plants or broken or blocked sewer mains can cause a sewage overflow into a recreational waterway. This can make the water unsafe for swimming.

An inter-government response plan is in place to make sure the public is aware when a sewage overflow occurs.

Will I get sick if I swim in water contaminated with sewage?

If you have contact or swallow water that is polluted with sewage it can make you very sick. Some illnesses may include:

  • Gastroenteritis (diarrhoea, vomiting);
  • Viral infections such as hepatitis; or
  • Infections of the skin or eyes.

How will I know if there has been a sewage spill?

Figure 1: Warning signs commonly posted during a pollution event.

When a sewage spill occurs in a natural waterway the community will be informed as a top priority. Warning signs and media releases will be issued to let you know the spill has happened. If you ever see a health warning sign along the river make sure you follow the advice and do not go swimming!

When will the water be safe to swim in?

After a sewage spill, experience has shown that it usually takes from 48 to 72 hours for a water body to return to a safe condition. Sometimes it can take a week or more. A number of factors will determine when a water body contaminated with sewage will return back to a safe condition. These include:

  • Salinity (the more salt the better);
  • Sunlight (the more sun the better);
  • Tidal movement;
  • Weather conditions; and
  • The volume of the spill.

The Environmental Health Directorate will not reopen a water body until it is considered safe for recreational purposes.

Can I eat fish or shellfish collected from water contaminated with sewage?

Evidence suggests that eating fish or crabs taken from water contaminated with sewage will not result in any known health effects as long as standard hygiene measures are followed. This includes washing your hands with warm water and soap after handling fish or crabs, thoroughly washing fish with clean water before cooking, and cooking using correct times and temperatures.

You should not eat any filter feeding shellfish (e.g. oysters, mussels) taken from water contaminated by sewage because:

  1. They feed by drawing water through a membrane and trapping food for digestion. Therefore, they draw contaminated water through the flesh that you'll end up eating - particularly dangerous if consumed raw because of pathogenic bacteria associated with sewage.
  2. Organisms like viruses (especially Hepatitis A and Norovirus) are trapped in the flesh of the shellfish and are not killed by the normal cooking process of shellfish.

The Environmental Health Directorate does not support the collection of wild shellfish from recreational waters surrounded by urban, industrial and commercial areas because the safety of eating wild shellfish can not be guaranteed.

What should I do if I see a sewage spill?

If you notice sewage draining into a natural water body you should immediately contact the Water Corporation on their Emergencies and Service Phone line on 13 1375.

Alerts Sign PLEASE NOTE: If you have been swimming in water that is known to be contaminated with sewage and you are experiencing symptoms of an upset stomach and diarrhoea, you are advised to go and see your usual medical practitioner for further advice.

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