Environmental health risks following cyclones and floods

Environmental Health efforts following a cyclone, flooding and excessive rainfall should initially focus on inspecting properties and public spaces across the impacted region, including remote communities as soon as access is possible, to assess damage and the condition of:

  • onsite wastewater systems
  • general sanitation
  • stray/leaking pesticide containers
  • evidence of mosquito breeding and
  • other potential hazards as outlined below.

A preliminary assessment along these lines can establish the type, extent and severity of environmental hazards that will need to be managed. It will also enable prioritising of resources to ensure that high risk or urgent issues are dealt with first, and provide an evidence base for recommendations that can feed in to requests for additional resources through the lead disaster response agency or processes.

Environmental Health Officers should also take a proactive role in increasing public awareness about the range of public and environmental health hazards that may result in and around a property and the general community following high flood waters.

The following public and environmental health hazards may be evident following a flood event. 

Environmental Health Officers should also read the Disaster and Emergency Management for Environmental Heath Practitioners (external site) produced by the Office of Health Protection of the Australian Government Department of Health.

Asbestos damage and contamination
Asbestos damage caused by flooded waters

Cyclones and flooding may result in damage to buildings that contain asbestos cement materials (ACM). Cyclones and/or major floods can cause breakage of asbestos material and often result in it being spread across a large area. In the case of cyclones some of the material may end up as small scattered fragments. Most asbestos cement material will remain well bonded and wet conditions may further reduce the release of asbestos fibres.

Role of Environmental Health Officers / authorised officers

Immediate response by local government

  • Identifying damaged asbestos is the first priority, followed by controlling access and disturbance of it. Any buildings or structures erected before 1990, should be suspected of containing asbestos, typically as flat or corrugated cement sheeting. 
  • Possible asbestos material should be assumed to contain asbestos and to be managed accordingly, pending the results of laboratory analysis. As a priority, briefing and providing guidance and reassurance to the concerned or affected public is important. 

Accessing asbestos contaminated properties

Ideally restrict access to asbestos contaminated properties only to officers with sufficient site risk information and appropriate personal protective equipment (PPE).

Some home owners may choose to do part of the clean-up themselves, but this comes with some potential risk and must be done by a professional asbestos removalist when asbestos material is crushed or material appears fibrous.

If home owners clean-up themselves they should follow the guidance provided by the Department on how to handle and wrap asbestos sheeting ready for disposal. Where there has been extensive damage the property may still need to be assessed and clean-up validated by an asbestos removalist.

For safety reasons, hire a licensed asbestos contractor (external site) to remove any materials that contain asbestos.

Asbestos professionals

Asbestos consultants – in the case of artificial surface and/or limited soil contamination, this professional should be an occupational hygienist (external site).

More information

Key contact 

Email doh.chemicalhazards@health.wa.gov.au for any questions regarding asbestos

Chemicals and other hazards
Cyclones and floods may have buried, moved or dangerous damaged goods including:
  • gas cylinders
  • containers of corrosives
  • oils
  • pesticides
  • pool chemicals
  • industrial chemicals.

Extreme care must be taken when handling any spills or containers of suspected poisons, chemicals or pesticides, especially if containers are damaged.

Spills or containers of these goods should be isolated until safe management has been arranged.

If there is damage to containers resulting in a leak or spill:

  • Contact the local fire services branch and any other relevant authority for expert assistance
  • Cordon off the area
  • Do not wash spillage down drains
  • If safe to do so, prevent spread of spilled material by using sand, earth or other commercial spill-containing products
  • Minimise the potential for presence of an ignition point or flame in case the chemical is flammable.

General tips for dealing with poisons, chemicals and pesticides

  • When handling dangerous goods wear personal protective equipment such as chemical resistant gloves, protective eyewear, enclosed footwear, long-sleeved shirts and trousers.
  • Ensure that if you are handling drums, you work up-wind and if there is a chemical odour present, wear a respirator with the correct chemically rated filter.
  • Generators and other fuel-powered equipment should stay outdoors, or be placed in a well-ventilated area to prevent the build-up of contaminant exhaust gases such as carbon monoxide.
  • Use an air monitoring device, such as a gas detector, to monitor the air in enclosed spaces where plant and equipment exhaust is generated.
  • Try to identify chemicals and their hazards using labels and markings.
  • If the label has been removed, seek expert advice and chemical identification from a waste management consultant
  • Separate chemicals from general waste, while identifying whether the container is damaged or not and if there is the risk of any chemical reactions. For example, oils and dry pool chlorine may cause a fire if brought together.
  • Take precautions to protect the area from further damage during the clean-up. This includes preventing mobile plant (earth-moving equipment) coming into contact with containers, particularly gas cylinders; prior to operation check all chemical processing and handling equipment affected by the flood, and ensure a qualified electrician checks electrical installations.
  • Contact your supplier regarding the safe return to operation for gas supply systems.

More information

Key contact

Email doh.chemicalhazards@health.wa.gov.au for questions related to chemical and other hazards

Contaminated swimming pools

Swimming pool flooded by flood waters

Role of Environmental Health Officers / authorised officers

Environmental Health Officers can help to educate the community about appropriate remediation for contaminated swimming pools. 

Swimming pools should either be emptied or kept chlorinated to prevent the water quality from deteriorating.

Contaminated swimming pools can be:

  • a source of odours and bacteria
  • a breeding place for mosquitoes
  • a risk to people who use them

Refer to the swimming pools inundated by flood waters for detailed information about restoring water quality. 

flooded swimming pool

Further information

Key contact

Email swimmingpools@health.wa.gov.au for swimming pool related queries. 

Onsite wastewater system damage
Damaged wastewater system caused by flood waters

Role of Environmental Health Officers / authorised officers

  • Environmental Health Officers have the legislative power to ensure a onsite wastewater system is safe for use and complies with the Health (Treatment of Sewage and Disposal of Effluent and Liquid Waste) Regulation 1974
  • Authorised officers can educate people about managing onsite wastewater issues on their properties. 

Health risk

On-site wastewater systems, such as septic tanks (primary treatment systems), secondary treatment systems (STS), aerated wastewater treatment systems (AWTS), and their land application systems, for example plastic leach drains, sprinklers and below ground drippers and connection pipes, can be damaged during a flood.

Damaged wastewater system caused by flood waters

Most wastewater systems should not be structurally damaged by flooding as they are below ground.

However, flood water may enter the wastewater system through the toilet, other fixtures or the overflow relief gully grate.

Flooding of the septic system may wash out solids from the tank causing blockages or system damage.

Onsite wastewater disposal systems should be pumped out by a licensed septic tank operator as soon as possible after the flood.

Refer to the wastewater after cyclones and floods on the HealthWA website.

Further information

Key contact

Email dwalert@health.wa.gov.au for questions related to wastewater.

Waste management
Environmental Health Officer's may need to have input into local government/emergency management identification/expansion of suitable waste disposal methods and sites to ensure correct disposal of waste (including asbestos), minimise potential for spread of contamination or impacts on water table etc.

A coordinated approach to the removal of waste by waste type and risk should be developed early and communicated clearly to residents. Wherever possible assistance should be provided by recovery crews/qualified waste management personnel with removal and disposal of hazardous wastes such as asbestos materials, chemicals and effluent.

Wastes and hazards likely to need to be disposed of include:
  • Asbestos containing materials and other building waste
  • Spoiled food
  • Rotting vegetation, green and organic waste
  • Effluent overflowing from septic systems
  • Damaged or compromised chemical containers (and contents)
  • Dead livestock, wildlife and other animals
Waste management issues may need to be coordinated in partnership with the Department of Water and Environmental Regulation (external site)
Rainwater tank contamination

Water in rainwater tanks can be contaminated during a flood by dirty flood waters.

If there is any risk of contamination residents should be advised not to use the water from the rainwater tank for drinking water purposes until it can be confirmed to be safe.

Using contaminated rainwater

If the water tank has been contaminated in any way, the water can still be used to:

  • flush toilets
  • water the garden
  • wash clothes (providing it will not stain clothes)
  • wash cars
  • fight fires.

Using any rainwater contaminated with ash or other debris to fill swimming pools or in evaporative air conditioners may clog filters and pumps. Contact the air conditioner, filter or pump manufacturer for advice.

Water testing

Testing of tank water is usually not necessary as contamination is usually obvious. 

To test the chemical quality of water in a water tank contact a National Association of Testing Authorities (NATA) (external site) accredited chemical laboratory.

Refer to the Department of Health Publication, Standard Drinking Water Assay (external site) for further information.

Refilling a rainwater tank

The tank may need to be drained and refilled with water from a commercial water carting company. Make sure that the commercial carting company:

Other sources of water

Water drawn from deep bores or wells should be safe to use.

Further information

Key contact

Email dwalert@health.wa.gov.au for questions related to rainwater tanks and water quality. 

Unsafe food that needs disposing

Role of Environmental Health Officers / authorised officers

  • Environmental Health Officers can educate the community and local food businesses about safely disposing of unsafe food.

When floods cause the power to go out, it generally means the food in a fridge or freezer will go off.

Refer to the power is off and so is my food (external site) for key information to support the public in disposing of unsafe food. 

Housing clean-up

Flooded house caused by flood waters

Cleaning up a house following a flood can be a daunting task.

Role of local government Environmental Health Officer

  • Local residents should be reminded to take extra precautions when entering their properties, and provided advice on appropriate clean-up procedures for various household items such as mattresses, linen and furniture.

Further information 

Poor recreational water quality

Role of local government Environmental Health Officer

  • Environmental Health Officers can educate the community about not swimming in recreational water bodies or consuming shellfish following a flood.

Recreational waters

After a flood, recreational waters – including lakes, rivers, estuaries and beaches – are likely to be contaminated with sewage, chemicals, nutrients and other pollutants.

There may also be unpredictable currents, fast flowing water and submerged hazards that are very dangerous.

People should not swim in or attempt to drive through floodwaters.

As a precaution people should avoid swimming in any recreational water body (such as a river or ocean locations near drains or a river mouth) for up to 7 days following a flood, but preferably not until bacterial water quality monitoring samples collected by local government confirms the water quality is safe for swimming.


Shellfish includes oysters, mussels, clams, pipis, scallops, cockles, and razorclams.

After a flood, it is almost certain that harmful microorganisms and toxins will be present in waterways (including rivers, lakes, estuaries and the ocean) due to run-off from the land. Shellfish should not be eaten from flood affected waters as they can make you sick.


Fish caught during flood periods should be rinsed prior to scaling and filleting.

Fish should be cooked thoroughly. You should avoid cross contamination between raw and cooked fish.

Further information

Mosquito management

Mosquito activity increases due to flood watersTidal storm surges and flooding associated with heavy rains, which often accompany cyclones, can produce extensive breeding habitat for mosquitoes. Residents of affected areas may be particularly vulnerable to mosquito exposure if their housing and insect screens have been damaged by a cyclone.

Refer to mosquitoes and cyclones for pre-and post-cyclone mosquito management measures to be considered by local governments to reduce the impact of mosquito activity following a flood. 

Members of the public can be referred to:

Snakes rodents and other wildlife

Like residents, snakes, rodents and other wildlife can become displaced during a flood.

As a result, they may seek shelter and food inside houses, storage sheds and other buildings.

Role of local government Environmental Health Officer

  • Local government Environmental Health Officers can help to educate the community about hazards to be cautions of before entire a property impacted by flood waters.


After a flood damaged structures and debris are more accessible to snakes.

When outdoors

Ensure you wear sturdy work boots, gloves, and long trousers to protect your legs and watch where you place your hands and feet when removing or cleaning up debris.

You should remove debris from around your home as soon as practically possible as it can attract rodents, lizards and insects on which snakes feed.

If you see a snake, step back from it slowly and allow it to proceed on its way – do not touch it.

Be aware of snakes that may be swimming in the water trying to get to higher ground, they may also swim towards a boat and attempt to gain entry.

They should be warded off with an oar or other long stake.

When indoors

If you find a snake in your house do not panic. Seek advice from the Department of Biodiversity, Conservation and Attractions on how to get in contact with the nearest licensed snake catcher.

If you are bitten by a snake you should seek medical treatment immediately.


If bitten by a red back spider:

  • wash the affected area well and soothe the pain with ice packs or clean iced water
  • do not apply pressure – this is not recommended for red back spider bites and often worsens the pain
  • seek immediate medical help.

For other spider bites:

  • wash the area with soap and water
  • apply a cold pack if the bite is painful
  • for most spider bites, no other first aid is necessary. Contact your doctor if symptoms develop or persist.

If possible and safe to do so, the spider should be caught for positive identification.

Read more on first aid for bites and stings.


To discourage rodents and the spread of disease:

  • remove food sources and items that can provide shelter for rodents
  • wash dishes and cooking utensils immediately after use
  • dispose of garbage and debris as soon as practically possible
  • lay rodent baits or traps.


To discourage flies and the spread of disease: 

  • do not let food and garbage build up as this becomes a breeding ground for flies
  • clean up food wastes as soon as possible.

Further information

Dead animal control

Role of Environmental Health Officer / authorised officer

  • Property owners should be advised to liaise with local government EHO prior to undertaking disposal or burial of any significant biomass, to ensure this is being done in a consistent and appropriate manner – and avoiding ongoing risks to water table, and surrounding environment. If this is a significant (widespread) problem, it is recommended that councils or recovery teams offer and coordinate assistance or services to facilitate an orderly disposal.

Following a natural disaster, many animals, particularly farm animals may not survive.

It is important to promptly dispose of these animal carcasses to prevent fly breeding, reduce odours, and protect surviving animals from disease.

Landholders should search their property for dead animals as soon as possible after a disaster, provided it is safe to do so.  In some cases, carcasses may have commercial value, so consider sending them to a rendering plant if possible.

If rendering is impractical, dispose of the dead animals on the premises. Where disposal or burial of any significant biomass, this must be undertaken in a consistent and appropriate manner in coordination with the local government.

Procedures to dispose of dead animals

  • Cover a carcass with crude oil or kerosene to keep away dogs, scavenging birds and vermin.
  • Well-fed pigs are the only animal carcasses that will burn satisfactorily. Old railway sleepers can be used as fuel. Burning of other carcasses is not recommended.
  • Bury other carcasses. Use earth moving equipment if it is available.
  • Choose a site where subsurface drainage will not reach water supplies.
  • Bury the carcass at least 90cm to 120cm deep, so predatory animals won't be able to reach them.
  • If quicklime (Builder’s Lime) is available, cover the carcasses with it before backfilling. Quicklime speeds up the decomposition process.
  • Work with the local government animal control officer for further guidelines.
Mould and dampness

Flood waters may increase mould and dampness problems in homes that will need to be managed to prevent health problems.

Indoor mould and dampness can also cause unpleasant odours and damage to building materials, contents and structures, which can lead to expensive maintenance or management costs.

Further information 

Last reviewed: 10-02-2021
Produced by

Environmental Health Directorate



Key agencies

Environmental Health Directorate support to local governments

The Environmental Health Directorate will endeavour to support the local government Environmental Health workforce impacted by large scale floods, with staff available to assist with any queries related to environmental health matters.

Phone (08) 9222 2000 or email ehinfo@health.wa.gov.au