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How pollution affects our catchments

About this lesson

There are many ways in which human activity can impact on the water draining from a catchment; such as homes and gardens, agriculture, industry, nature reserves and transport.

Year level: 3, 4

Theme: Water supply

Learning objectives

Students can:
  • explain what a catchment is
  • discuss ways to help keep our water clean
  • present their ideas to the class or wider school community.

Curriculum links


  • Science knowledge helps people to understand the effect of their actions ACSHE051 ACSHE062


  • Use interaction skills, including active listening behaviours and communicate in a clear, coherent manner using a variety of everyday and learned vocabulary and appropriate tone, pace, pitch and volume ACELY1792


  • OI.9 - Sustainable futures result from actions designed to preserve and/or restore the quality and uniqueness of environments.

Things you will need

  • Story of a catchment activity sheet 
  • 2 buckets (to represent the river)
  • 4 large ice cream containers (1 for each group)
  • Yoghurt pots (1 for each student)
  • Food colouring or paint
  • Labels: Home, school, farmers, industry & river
  • Extra pollution (e.g. grass clippings, soil & plastic)

Lesson description

Australia is the driest inhabited continent and therefore water is one of the most important elements for our survival. Each one of us lives in a catchment and therefore can affect the quality of our waterways either indirectly or directly.


  • Use the shower example below to explain to students what a catchment is.

    A shower is like a catchment

    The water from the showerhead represents rainfall and your head is like the top of the catchment. As water passes over your body, it picks up soap, grease and dirt. By the time the water reaches the drain its quality is not the same as when it 'rained' or left the showerhead. The same applies to a river flowing through a catchment. It picks up all sorts of things along the way including pollutants.

    So just like when we have a shower, pollutants act the same way, they mix with the water moving across the catchment and are deposited in the lowest point. This can lead to the deterioration of water quality.

  • As a class brainstorm who may use water from a river as it travels down through to a catchment and record the answers on the board (e.g. homes, schools, farmers, industry, fishermen, people who use boats).


Explain to students that they will role-play a story to further explain what a catchment is and how it can become polluted.

  • Divide the class into 4 groups and give them a label as a water user (home, school, farmers, and industry).

  • Take the students outside and give each group an ice cream container.

  • Keep the first bucket full of clean water which represents the river or dam.

  • Each group form themselves into a chain (to represent the water as it travels along the river).  Have the first person in each chain stand next to the other bucket

  • Using yogurt pots, transfer the water from person to person until their container is half full. If you run out of water in your bucket you may have to 'make it rain’ again to fill it up. Explain that this is what happens in Australia during the summer months and is why we all need to conserve water.

  • Tell the Story of a catchment. As you tell the story, each group takes turns to ‘pollute’ their water with a few drops of paint or food colouring or even grass or leaves to represent the pollution.

  • At the end of the story, each group form their chain to transfer the polluted water into the end bucket to represent the river at the end of its journey. The others watch the effects then take their turn.

Reflect & summarise

  • What happened to the water in the final bucket?
  • What did each group feel like when their water got dirty and made the river dirty?
  • Which things that polluted our river could have been avoided?
  • Ask each group to produce a poster for their user type, 'Keep our water clean'. Display some of the posters on the interactive whiteboard or the schools website.

Teacher background information

What is a catchment?

A catchment area is a surface area from which runoff flows. A catchment area might include a lake, a reservoir (or dam), a stream or any other water body and areas where water soaks into the ground and recharges as groundwater.

Pollution of catchments

There are many ways in which human activity can impact on the water draining from a catchment. This includes homes and gardens, agriculture, industry, nature reserves and transport.

Many have a negative impact on water quality, such as nutrients from agricultural areas, waste from industrial areas, oil and fuel from roads and wastewater from homes. Everyday activities such as driving in a car or fertilising our gardens can also lead to pollution of water entering dams and waterways.

Groundwater contamination

Much of the Perth area is covered with sandy, porous soils. Most private wells (bores) are located within this shallow aquifer system, as are some Water Corporation bores that supply the Integrated Water Supply Scheme with drinking water. Perth wetlands are often an expression of the shallow aquifer, where the water table is visible in low-lying areas.

Rainfall seeps through these sandy soils into the water table where it collects in groundwater aquifers. Pollutants spilled on the ground, or leaking from storage vessels, have the potential to contaminate groundwater aquifers through seepage. Groundwater contamination in the shallow aquifer system can endanger community health and threaten the environment; especially the fauna and flora of wetlands.

Controlling groundwater contamination

Water Corporation regularly monitors the quality of groundwater used for public water supply, to ensure that scheme water meets the requirements of the Department of Health, which are based on the Australian Drinking Water Guidelines (2011).

Fortunately, the Perth region has not suffered widespread groundwater contamination; there have been only localised areas of contamination at some sites in industrial areas and at petrol stations (where tanks have rusted and leaked fuel).

It is said that groundwater contamination has a long memory: it can take decades to hundreds of years for contamination to disperse naturally. For this reason, ‘prevention is better than cure’ is the prevailing policy.

Potential sources of groundwater contamination

  • Septic tanks – high levels of micro-organisms from septic tanks pose a health risk if they enter groundwater used as drinking water. Contaminated groundwater can also contribute excessive nutrients to wetlands and watercourses, resulting in algal blooms that kill fish and aquatic animals and may be harmful to human health. Septic tanks must be set back a safe distance away from bores or reservoirs used to supply drinking water. The Water Corporation is actively reducing the number of septic tanks in the Perth region by installing deep sewerage (through the Infill Sewerage Program) in non-sewered urban areas.
  • Fertilisers and pesticides – excessive or incorrect use of fertilisers and pesticides from horticultural industries, market gardens and domestic gardens can be a source of groundwater contamination. Slow-release fertilisers, which gradually break down over time, are recommended where practical and new horticultural developments are discouraged in environmentally sensitive areas (e.g. the Peel-Harvey catchment).
  • Solid and liquid waste disposal – in the past, community and industrial wastes in the Perth region were occasionally disposed of in sandy depressions, which in some cases resulted in groundwater contamination. Waste disposal is now allowed only at properly located, appropriately constructed (e.g. impervious-lined), operated and supervised waste disposal sites. There are heavy penalties for the illegal dumping of waste materials.
  • Accidental leakage – leakage of industrial chemicals and petrol from surface and subsurface tanks can pollute groundwater and surface water. Chemical transport vehicle accidents can also cause contamination when runoff enters drainage systems that discharge into streams, wetlands or rivers. There are now strict controls on the construction of underground petroleum storage tanks in drinking water catchments and other sensitive areas, and groundwater quality at the sites must be monitored. Above-ground petroleum storage tanks with proper spill protection (e.g. double containment around pipe work) are now used in environmentally sensitive areas.
  • Saltwater intrusion – groundwater quality can be seriously affected by the intrusion of salt water from the ocean or an estuary. Saltwater intrusion occurs when fresh groundwater supplies are over pumped, causing the underlying salt water to be drawn upwards and inland. Bores sunk in coastal and riverfront areas should just penetrate the water table and be pumped at low rates so as to avoid drawing up the deeper saline water. Developments (e.g. horticulture) requiring large quantities of groundwater from wells in drinking water catchments are discouraged from using the shallow aquifer.


Did you know?

It can take up to hundreds of years for groundwater pollution to disperse naturally.

Key vocabulary

  • Catchment: The surface area from which runoff flows, sometimes via drainage systems, to a river, dam or wetland
  • Permeability: The ability of a fluid to move through soil or limestone rock
  • Pollution: The addition of harmful things to the environment
  • Saline intrusion: The forcible entry of salt into water
  • Water quality: How safe water is for drinking and the environment