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Impacts and Problems

The Georges River catchment is one of the most highly urbanised catchments in Australia.  Whilst this means that lots of people get to experience and enjoy the river, it also means that there are many different issues that are impacting upon the health of the catchment.

There are many different aspects of our day to day lives that have an impact on the catchment.  While each of us individually has a small effect on the health of the river, these small impacts combine throughout the whole catchment to significantly effect the health of the river. 

One of the main causes of poor river health is stormwater pollutionWeeds, introduced animals and erosion also significantly contribute to an unhealthy catchment, but we have some tips that will help you make a difference!

Stormwater pollution

In urban and semi-urban areas, rain that falls on the roof of your house, or collects on paved areas like driveways, roads and footpaths is carried away through a system of pipes known as the stormwater system.  Water in the stormwater system flows directly from the drains you see on streets to our creeks and rivers.  In some cases the water is partially filtered and treated by stormwater treatment devices, however most of the time the water remains untreated.  This means that anything that gets washed down the drains such as oil, litter and pesticides ends up in our waterways.  Weeds, soil and mulch can also easily be washed away in rain.

Because of the impact that stormwater pollution can have on our rivers and beaches, water quality is often significantly worse after rain.  Sometimes you may even be advised not to swim due to the health risk that stormwater pollution poses. Imagine what this is doing to our environment!

Click on this link to an ABC Catalyst Program segment, which describes the impacts of stormwater on water quality


Weeds have a significant impact on our catchments and are a threat to native flora and fauna as well as the health of our waterways.  Weeds:

  • Smother and out-compete native plantsLantana
  • Destroy the habitat of native animals
  • Reduce water quality
  • Choke waterways.

Most weeds that are in our bushland areas today have escaped from people backyards.  Their seeds and cuttings are carried by the wind or animals, or even swept away with the stormwater when it rains.  Frequently, prunings, cuttings and grass clippings are dumped in the bushland too, allowing weeds to quickly invade and spread.

There are two categories of weeds:
Noxious Weeds - These weeds threaten human and animal health, agricultural production, and the environment (including natural resources such as waterways and water supplies).  By law, noxious weeds must be controlled.  On private land the responsibility lies with the owner and/or occupier of that land.

To find out which weeds are listed as Noxious in your Council area visit the NSW Department of Primary Industries.

Environmental Weeds - Environmental weeds invade bushland, thereby reducing its environmental value.  They have few predators and usually produce vast quantities of seed, and so out-compete or smother native plants.  They are particularly successful in disturbed areas where soil nutrient levels are high, such as areas affected by stormwater pollution or the fringes of bushland areas bordering residential properties.

Introduced AnimalsGambusia

The Georges River Catchment is unfortunately threatened by many introduced animals.  Cats and foxes are a big threat to native animals, preying on birds, small mammals and reptiles.  Deer, rabbits and some birds also impact on our catchment to varying degrees including damaging vegetation, causing erosion.

In many of the freshwater ponds and wetlands in the Georges River catchment European Carp and Mosquito Fish (Gambusia holbrooki) cause significant damage.

Mosquito Fish (also known as the Plague Minnow) can live in most aquatic conditions and once in a waterbody, are extremely difficult to remove.  It is currently illegal to release gambusia into ANY waterbody in NSW. Despite the impacts of this fish on the natural environment, gambusia are still sold in pet shops as feeder fish or to put into backyard ponds.

Carp also impact the health of freshwater aquatic ecosystems by increasing water turbidity and nutrient concentrations, destroying aquatic plants, and potentially causing the recurrence of toxic blue-green algae blooms. They also breed rapidly, eliminating native fish, tadpoles and other small lifeforms.

Erosion and SedimentationSediment from house

You may have noticed that many of our waterways are becoming shallower and muddier - something which may be very noticeable after rain.

When the ground is left bare by human activities including clearing, building (and related activities) and vehicle use such as 4WD's and trail bikes the soil is easily washed away when it rains.  Examples of this can be seen between Sandy Point and Alfords Point as sediment from the ridges washes into Mill Creek and then into the Georges River.  This erosion removes the fertile topsoil and the soil that is washed into waterways can contain plant nutrients, minerals, organic matter and seeds. It can also contain pesticides and toxic heavy metals.

When soil, sand, dust, cement, paint and building debris reach the waterways, they can:

  • increase the risk of flooding;
  • block drains;
  • spread weeds to bushland;
  • result in algal blooms;
  • cause health problems for swimmers;
  • smother and suffocate water plants and animals and impact on their ability to reproduce.

A single residential building block can lose four truckloads of soil in one storm!