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stormwater pollution

Sources of stormwater pollution

Every year, billions of liters of stormwater flow down drains and into our river and creeks. Most of the water, however, is polluted with:

Litter

Litter recovered from a litter trap

Litter comes from bins that are too full, especially in schools and shopping centres. It comes from rubbish thrown on streets and from cars and train. It comes from cigarette butts carelessly left on streets. It also comes from rubbish and other items that are blown off bins, factories, shops or landfill sites.

When it rains, stormwater carry the litter from streets, reserves and parks into drains and eventually, into our rivers and creeks.

Litter makes our rivers and creeks look ugly. It is also a real danger to the animals and plants living in our rivers and creeks.

Parks Victoria operates 14 litter traps on the Yarra. These litter traps collect about 1800 cubic metres of litter, rubbish and organic matter which are washed into the river each year. This includes plastic and glass bottles, syringes, drink cartons, cigarette butts and lighters.

We are working with Parks Victoria to remove litter along the Yarra. However, it is everyone's responsibility to dispose of our litter responsibly.

Pathogens

Pathogens
The amount of E. coli bacteria in the Yarra River is generally lower than other rivers that run though big cities around the world.

Because our rivers are open, microorganisms (tiny single cell animals) can be washed into them from farms and towns. Even pristine rivers will contain some microorganisms.

While many microorganisms are harmless, some can make us sick. These microorganisms are called pathogens. These pathogens enter our rivers and creeks from animals in the catchments, from garden fertilisers and manure, sewer overflows and from septic tanks which are poorly maintained.

A way of finding out if there are pathogens in our rivers and creeks is by counting the amount of a type of bacteria call Escherichia coli, or E. coli in a sample of water. E. coli bacteria are not thought to be harmful, but it can be used to tell us if there are pathogens are in the water.

As Melbourne's sewerage system continues to improve, the amount of E. coli bacteria in the lower reaches of the Yarra River have decreased. In fact, the amount of E. coli bacteria in the Yarra River is generally lower than other rivers that run though big cities around the world.

Toxicants

A litter trap on the Yarra River

Toxicants are things that are poisonous at certain concentrations. Many of the things we use or have outside the house contain toxins. These include things that are made from petroleum, like oil and petrol, or things that have mercury, copper or arsenic (called heavy metals) in them, like paints or rust. Other things that contain toxicants include pesticides, herbicides and septic tank cleaners.

These toxicants can be washed into our rivers and creeks, if we empty paint or petrol down the stormwater drain. Toxicants from pesticides and herbicides can also be washed from the ground and into our rivers and creeks.

Toxicants can affect the life-cycle of an animal or weaken an animal's ability to fight off predators. Toxins can also build up in fish, plants and other aquatic animals, potentially killing them or animals that eat them.

Nutrients

Wetlands
Wetlands act as natural filters by removing litter, suspended solids (like dirt and sand) and nutrients from stormwater, before it enters our rivers and creeks.

Plants and animals need nutrients, like nitrogen or phosphorus, to grow. But because our soils, rivers and creeks generally do not have a lot of nutrient in them, our plants and animals have adapted to these conditions. Therefore, they are not used to having lots of nutrients in their environment.

Nutrients can enter our rivers and creeks through fertilisers, organic manure or food scraps. As they break down, they either release nitrogen or phosphorus compounds. Too much phosphorus in our rivers and creeks, or too much nitrogen in our seas, can mean that there will be an explosion of plant growth. Too much plant growth can choke our rivers and creeks, and lead to large variations in the amount of oxygen in the water. During the day, there would be lots of oxygen, but at night, the amount of oxygen would decrease drastically. This variation means that fish and other aquatic animals which depend on oxygen to life, are affected.

A 1996 CSIRO study supported by Melbourne Water recommended that the amount of nitrogen entering the Bay (from the stormwater system and from treated effluent) can be significantly reduced. One of the ways we are doing this, is by constructing wetlands. Wetlands act as natural filters by removing litter, suspended solids (like dirt and sand) and nutrients from stormwater, before it enters our rivers and creeks.

Suspended solids - fine particles in water

Turbidity
Turbidity in our rivers and creeks can also slow down plant growth as it blocks sunlight essential for plant growth. It also lowers the amount of oxygen in the water. This affects the survival of aquatic animals.

Fine particles like soil or dirt can be washed from bare river banks into our rivers and creeks. They can also be washed from streets into our drains, and eventually into our rivers and creeks. This makes our rivers and creek look muddy or turbid.

Turbidity - the amount of very fine particles suspended in water (suspended solids) - can cause sedimentation in slow moving rivers or creeks. In sedimentation, these very fine particles would sink to the river bed, and smother the plants and animals that live at the bottom of the river. It can also cause flooding, and navigational problems for boats.

Turbidity in our rivers and creeks can also slow down plant growth as it blocks sunlight essential for plant growth. It also lowers the amount of oxygen in the water. This affects the survival of aquatic animals.