Stormwater pollution comes from different places. There are three main kinds:

  • litter – like cigarette butts, cans, food wrappers, plastic bags and paper
  • natural pollution – like leaves, garden clippings and animal waste
  • chemical pollution – like fertilisers, oil and detergents.

Different types of pollution have different impacts on the environment. In addition to contaminants in stormwater, the extra volume of water due to greater run off can lead to erosion and scouring in streams.

Sources and impacts of stormwater pollution

  • Sediment

    Sediment comes from:

    • land surface erosion 
    • pavement and vehicle wear 
    • building and construction sites 
    • illegal spills and discharges 
    • organic matter – like leaf litter and grass 
    • car washing 
    • weathering of buildings and structures 
    • atmospheric deposition. 

    Sediment impacts the environment by:

    • reducing the amount of light in the water available for plant growth – reducing food supplies for other organisms
    • clogging and damaging sensitive tissues – like fish gills 
    • suffocating organisms that live on or in the bed of lakes and streams. It forms thick deposits when the suspended material settles out. 
  • Nutrients

    Nutrients come from:

    • organic matter 
    • fertiliser 
    • sewer overflows
    • septic tank leaks 
    • animal faeces (poo)
    • detergents (car washing) 
    • atmospheric deposition 
    • illegal spills and discharges.  

    An increase of nutrients in water encourages aquatic plants to grow.

    This causes excessive growth of aquatic weeds and algae. These may choke lakes and streams and lead to dramatic daily fluctuations in dissolved oxygen levels. 

  • Oxygen-demanding substances

    Oxygen-demanding substances come from:

    • organic matter decay 
    • atmospheric deposition 
    • sewer overflows
    • septic tank leaks 
    • animal waste
    • illegal spills and discharges.  

    If oxygen is used up faster than it can diffuse into the water from the atmosphere, there can be a drop in oxygen levels. This may kill fish and other aquatic organisms. 

    If all oxygen in the water is used up, it can cause unpleasant odours.

  • pH

    pH comes from:

    • atmospheric deposition
    • illegal spills and discharges 
    • rotting of organic matter
    • roofing material wearing away.  

    Changes in acidity can harm plants and animals. 

  • Micro-organisms

    Micro-organisms come from:

    • animal waste 
    • sewer overflows
    • septic tank leaks 
    • organic matter decay. 

    These can cause disease, including hepatitis and gastroenteritis.  

  • Toxic organics

    Toxic organics come from:

    • pesticides 
    • herbicides 
    • illegal spills and discharges 
    • sewer overflows
    • septic tank leaks.

    They can poison living organisms or damage their life processes. 

  • Heavy metals

    Heavy metals come from:

    • atmospheric deposition 
    • vehicle wear 
    • sewer overflows
    • septic tank leaks 
    • buildings and structures wearing away
    • illegal spills and discharges. 

    Heavy metals poison living organisms or damage their life processes in some other way. They stay in the environment for a long time. 

  • Gross pollutants (litter and debris) 

    Gross pollutants come from:

    • pedestrians and vehicles 
    • waste collection systems 
    • leaf-fall from trees 
    • lawn clippings 
    • spills and accidents. 

    Gross pollutants can be unpleasant to look at. Animals can eat and choke on litter.

  • Oils, detergents and shampoos

    Oils, detergents and shampoos come from:

    • asphalt pavements 
    • illegal spills and discharges 
    • leaks from vehicles 
    • car washing 
    • organic matter. 

    They're highly toxic to fish and other aquatic life.

  • Increased water temperature

    Increased water temperature is caused by:

    • runoff from solid surfaces
    • removal of plants near the water’s edge. 

    High temperatures are lethal to fish and other aquatic organisms. Increased water temperatures encourage nuisance plants and algae to grow. This can lead to lower levels of dissolved oxygen, which can threaten other aquatic life.

  • Increased water flows

    Urban areas have a lot of hard surfaces, such as roads and roofs. This results in rapid changes in water levels in rivers and creeks every time it rains. The stormwater brings not just contaminants and litter, but also causes erosion of the bed and banks, and scouring of the animals and plants that live there.

Reviewed 25 October 2021