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What is stormwater?

Stormwater is rainwater that runs off hard surfaces and enters the drainage system. The drainage system is designed to reduce flooding by redirecting the stormwater runoff from our streets and gutters into nearby streams, creeks, rivers, estuaries and finally the ocean.

As our population increases and urban development continues, stormwater runoff increases. This is due to the building of more hard and impenetrable surfaces like roads, driveways, car parks, roofs and paving. Therefore, more stormwater runoff enters the drainage system and into waterways.


What is the cause of stormwater pollution?

As stormwater runs freely it picks up pollutants along the way. This mix of stormwater and untreated pollutants enters the stormwater drain system and from there into rivers and ultimately Port Phillip Bay.

The main components of stormwater pollution are:

  • Chemical pollution; heavy metals, hydrocarbons, pesticides, fertilisers, or detergents
  • Litter; cigarette butts, cans, food wrappers, plastic bags or paper
  • ‘Natural’ pollution; leaves, garden clippings or animal faeces
  • Bacterial pollution from leaking, broken or overflowing sewers.

A list of stormwater pollutants can be found on the EPA website.


What are the impacts of stormwater pollution?

Around 540,000 million litres of stormwater flows into Port Phillip Bay each year. Stormwater washes 14,000 tonnes of sediment, 650 tonnes of nutrients such as nitrogen from fertiliser, litter, heavy metals and bacteria into the Yarra River each year.

Stormwater can impact the environment in two main ways. Firstly, the high flow associated with stormwater entering waterways creates a physical disturbance. Sediment clouds the water and makes it difficult for aquatic plants to grow. Stormwater can also wash away flora and fauna from their natural habitats.

Additionally, nutrients and pollutants are picked up and transported by stormwater into our waterways where they can cause a range of adverse impacts:

  • Excess nutrients can cause algae blooms. When algae die, they sink to the bottom and decompose in a process that removes oxygen from the water. Fish and other aquatic organisms can't exist in water with low dissolved oxygen levels.
  • Germs can wash into swimming areas and create health hazards, occasionally making beach closures necessary.
  • Litter - plastic bags, six-pack rings, bottles, and cigarette butts washed into waterways can choke, suffocate, or disable aquatic life like ducks, fish, turtles, and birds.
  • Household hazardous wastes like insecticides, pesticides, paint, solvents, used motor oil and other auto fluids can poison aquatic life. Land animals and people can become sick from eating diseased fish and shellfish or ingesting polluted water.  

Litter pollution from stormwater dispersing into a natural environment

Stormwater pollution. Image source. EPA Victoria

How is stormwater being managed?

Actions to improve our environment

Local councils have a significant role in improving the environmental management of urban stormwater. EPA provides support and guidance to assist councils meet their obligations. Improvements in recent years include the development of stormwater management strategies, especially for new developments and drainage systems and new measures such as infrastructure upgrades, to prevent the release of wastewater into the stormwater drainage system.

Stormwater as a resource

While stormwater can be an issue, it can also be an asset.

Stormwater is an excellent alternative to using valuable drinking water. It is easy to capture, manage, store on-site and is less expensive than drinking water. Harvesting stormwater and recycling rainwater can be utilised to sustainably supply water to our communities for non-drinking purposes.

Stormwater has been identified as a valuable resource for our city, with a focus on urban stormwater harvesting schemes. This involves the collection, treatment, storage and use of stormwater runoff from urban areas for irrigating sports and recreational grounds, schools, apartment blocks and construction sites. This differs from rainwater harvesting as the runoff is collected from drains rather than roofs.

By collecting rainwater, the amount of stormwater runoff decreases, potentially reducing nuisance flooding and environmental damage. Rainwater use in and around the home can be used for watering the yard, toilet flushing and car washing. For further information EPA recommends ways of harvesting stormwater.

Water Sensitive Urban Design (WSUD) is an effective and innovative approach for managing stormwater. WSUD looks to manage the impacts of stormwater from development and urbanisation by integrating small scale, local water management solutions into communities. Design approaches include infrastructure and planting materials that slowly filter and treat stormwater pollutants with the aim of protecting waterways from pollution. These can include:

  • Grassed or landscaped swales
  • Rain gardens and infiltration trenches
  • Wetlands,sediment ponds and gross pollutant traps
  • Rainwater tanks – (small tanks for homes and larger tanks for community assets like sports fields and parks)
  • Grey water harvesting and reuse
  • Green roofs and urban forests
  • Porous pavements.  

Water sensitive urban designs, native vegetation to reduce pollutants and slow stormwater flow

Landscaped swales. Image source: Melbourne Water 

Informing Communities

In the event of a stormwater event, alerts will be placed on the Beach Report and Yarra Watch. Alerts contain important information about water quality and other events occurring in the bay and allow you to make informed choices about using the Yarra River and Port Phillip Bay for recreation.

As a precautionary measure it is advised not to swim 24-48 hours after heavy rain.


Environmental citizenship

Through strong environmental partnerships the Victorian government aims to encourage a new sense of environmental citizenship, where individuals, communities, businesses and other organisations take a more active and shared responsibility in efforts to support our environment.


What you can do to help protect our waterways

The best prevention of stormwater pollution is to reduce contaminants from entering the drainage system through the following actions:

  • Washing your car: Wash your car on a grassed area rather than on hard surfaces and consider using low environmental impact detergents.
  • Fixing your car: If you are changing the oil in your car check with your local council regarding chemical collection services, rather than tipping oil down the drain.
  • Composting: Rather than allowing the accumulation of organic material in gutters which could be swept down into the drainage system, use it as compost or garden mulch.
  • Disposing of litter: Put litter in the bin, litter dropped in the streets will be transported into drainage systems, onto our beaches and into our waterways.
  • Gardening: Consider using low environmental impact pest control products when outside.

Young boy and urban rain garden

Rain garden. Image source. Melbourne Water

For additional information on how you can help refer to EPA’s website with suggestions on what can we do about stormwater pollution?


Melbourne Water recommends effective approaches for reducing the flow and treating nutrients in stormwater runoff through various methods such as creating rain gardens around the home.


There are many organisations and groups involved in maintaining the water quality of the Yarra and the Bay. If are interested in knowing more about how you can get involved, go to the How you can help page on this website.

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