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Water quality

Water quality spans a wide range of visible and invisible phenomena.

Zac Kirby inspecting at the river's edge on Billa Downs Station near Euston in New South Wales during the 2007 drought.

Maintaining the quality of water is crucial for a healthy environment and for providing suitable drinking water for communities. Water quality may also impact the productivity and profitability of agricultural activities, and recreational use of our waterways.

Healthy water has appropriate levels of nutrients, oxygen and other gases, and is of a suitable temperature to sustain life.

The way humans use the land and water can cause water quality degradation. Major indicators of a decline in water quality are high salinity; low dissolved oxygen (sometimes leading to blackwater); inappropriate temperatures; build-up of blue-green algae, excessive nutrients and/or suspended matter; toxicants and incorrect pH or salt levels.

There are a number of management activities in the Murray–Darling Basin that can minimise the effects of physical, biological and chemical threats to the quality of the Basin's water.


By the end of this resource, students will understand:

  • the factors that influence water quality
  • the effects of poor water quality
  • management options for some water quality issues.

Curriculum focus

How to use this resource

There are four water quality issue investigations in this resource. The topic exploration phase can be done as a group activity in one lesson, and followed with one elaboration activity of your choice (from several options provided). However, the material can also be used as a unit of work incorporating all the activities and consolidating learning by playing the online ABC Science educational game Catchment Detox, which lets students play the role of catchment managers. Using the content this way brings in ACSIS107, ACHASSI126 (data analysis and interpretation) and also potentially digital technology ACHGS049, ACTDIP026, ACTDIP027.


Make mixtures in two beakers:

  • One containing black tea (teabag, water), a little bit of dirt, few leaves, twigs etc.
  • One containing salt and white vinegar.

Check the pH of both (using test strips). Aim for the one containing dirt/tea to be 7 in pH (you may need a small amount of bicarb) and the vinegar solution should be only around 2.5 (do not make the water visibly cloudy with the salt).

Have ready at front of class, along with some extra pH test strips.

Even better, if experienced with using universal indicator, prepare two measuring cylinders of it.

1. Engage with the topic

Ask students ‘which one is dirtier?’ You could also ask ‘if you lived permanently in water, which one would you rather be in?’

Have two students come to the front and use the pH strips to test the solutions. (Or drop some of each into universal indicator). After getting the results, ask students if they have changed their mind.

Discuss: what is water quality?

Healthy water does not harm plants or animals (including people). It may contain many living organisms, dissolved nutrients, bits of organic matter (leaves, bark, dead creatures), soil, sand, trace metals from weathered rocks or brought down in rain and even some salt—yet still have the correct acid/alkaline balance (pH) and provide a healthy habitat. Very importantly, it will have a suitable amount of oxygen dissolved in the water and be of appropriate temperature.

Ask: What things do you know that decrease water quality?

2. Exploring water quality problems

For each of the four topics, students could work in groups. They research and complete a worksheet.



Teaching notes Worksheet answers
Students investigate:

Managing water: salinity

Salt of the Earth

Salt is a natural feature of the environment. It is formed from ancient ocean sediments and the weathering of rocks. Salt moves through the rivers of the Murray–Darling Basin.

Salinity is a word used to describe how much salt is in water.

Many organisms cannot live in water sources that have a high salt concentration.

Salty water is also less useful in agriculture.

The removal of deep-rooted vegetation can allow salty water tables to rise to the surface, causing saline soils and killing crops (this is known as dryland salinity).

Irrigation on top of water tables can do the same thing (irrigation salinity).

Urban salinity is a combination of both processes, and can occur when natural drainage is interfered with, parks & gardens are over-watered, or effluent and waste water is not contained or treated properly.

Note: dredges run most of the time at the Murray mouth to try and keep it open and allow a bit of salt to escape.

1.a. Before land clearing.

Salt is sitting just at the top of the water table. The tree roots are keeping the water table down.

1.b. After land clearing. Salt has risen because the water table has risen since there are no deep roots sucking it up.

2. Replanting salt-tolerant trees can help improve dryland salinity.

3. Salt naturally left rivers when sufficient flow flushed it out to sea.

4. This doesn’t happen because flow is diverted to human uses along the way, so only low flows reach the sea.


Teaching notes Worksheet answers
Students investigate:

Managing water quality: blue-green algae

Nutrient enrichment of waterways is called eutrophication. The two main nutrients that cause problems in rivers are nitrogen and phosphorous; usually entering the waterways as runoff from farms or forestry operations. Sewage is another source.

We apply nitrogen and phosphorous to crops as fertilizers. Another source of nitrogen and phosphorus is animal droppings.

When it rains, the nutrients can be carried into nearby water-sources and contribute to algal blooms.

Various algae are always present, but when sufficient heat combines with high nutrient levels they thrive. Blue-green algae (cyanobacteria) grow faster than other types. They also boom even more when flows are low and the water still.

Cyanobacteria also generate toxins that are a health risk to humans and livestock.
  1. Eutrophication is when a body of water becomes overly enriched with minerals and nutrients that induce excessive growth of plants and algae. This process may result in oxygen depletion of the water body.
  2. Phosphorus, nitrogen.
  3. Agriculture (fertilisers), aquaculture, septic tanks, urban wastewater, urban stormwater runoff, industry, and fossil fuel combustion.
  4. Cyanobacteria (or just bacteria). Species include Dolichospermum and Microsystis.
  5. Plants and animals die – especially fish.
  6. Blue-green algae
  7. For humans and livestock, the toxin can cause liver damage, stomach upsets, nervous system disorders, skin and eye irrigations. Wildlife and pets can be poisoned, even killed.
  8. The only real current solution is to flush water down the rivers and wash the bloom away. Preventative solutions include using less fertiliser, detergents and agricultural products that contain phosphorus or nitrogen.
  9. The cycle should show bacteria in water, nutrients washing off farmland or towns, sun (heating of water), slow-flowing water, and then algal growth. Students may also show fish death or similar. An example is provided in linked content.

Low oxygen

Teaching notes: Worksheet answers
Students investigate:

Blackwater visual explanation

For more detailed information, see Managing water quality: blackwater.

Show the blackwater visual explainer to this group of students.

Water contains dissolved oxygen, critical to aquatic life. Oxygen levels are naturally higher in fast-flowing water and in cold rather than warm water.

Oxygen levels are also affected by the presence of lots of organic matter, such as leaf litter and bacteria. This is because as carbons decay, they consume oxygen.

Blackwater can occur during floods, which wash organic matter into waterways. In the past, floods happened more often, so this process occurred without too much harm. Now with dams and human water use, they are rare. Therefore by the time a flood large enough not to be contained in dams occurs, floodplains may have accumulated many years of carbon debris. As it rots it can blacken the water, and as bacteria decompose it, oxygen levels drop significantly, and unfortunately many fish die of asphyxiation.

  1. Eutrophication.
  2. Organic matter (leaves, sticks); oxygen.
  3. Carbon compounds/tannins released when organic matter rots are staining the river on the left (river on right has high turbidy/is muddy).
  4. food, breed/hide
  5. It’s been too long between floods, so there’s too much organic matter and when it washes into the rivers and breaks down it uses up all the oxygen in the water.
  6. Dams now contain most floods, people using lots of water keeps river levels low.
  7. Consequences include toxins (tummy/skin/eye problems or even death).
  8. While there is no instant solution, in limited places fresh oxygenated water can be pumped/piped in to provide a refuge for fish. Over the long-term solution is to use environmental water to flush floodplains more often.
  9. Diagram should show concepts as in example ‘blackwater diagram’ in linked resources.

Acidity and turbidity

Teaching notes Worksheet answers
Students investigate:

"Check the pH before jumping into this wetland!" (ABC)

  • pH is a measure of how acidic or alkaline water is. The pH scale goes from 0 – very acidic – to 14 – very alkaline. Something that has a pH of 7 is ‘neutral’, or neither acidic nor alkaline.
  • Living things in our rivers and wetlands (and humans) prefer pH closer to the neutral.
  • Sulphides in soil at the bottom of wetlands and rivers is natural.  However, if these are exposed to air (like in drought or when human uses reduce flow), they turn to sulphuric acid. If this happens for long enough, heavy metals (including aluminium and arsenic) are also released from the sludge. This kills everything!

1.a. acid-suphate soils/ high acidity/ low pH

1.b. no lower than 6.5

1.c. 1.6

1.d. to 1.f. See notes at left.

1.g. The best solution is returning the wetland (or creating a man-made one). Adding lime can neutralise the acid.

Water quality: turbidity (Smithsonian Environmental Research Centre)

Turbidity is a word that describes how murky or clear water is. Higher turbidity = cloudier or murky.

A main cause of increased turbidity is erosion; whereby soil and plant matter gets washed into waterways.

The flow of water is a factor. Slow moving water makes it easier for particulate matter to settle out of the water column.

Turbid water can prevent light from reaching the plants and animals living in a river. This can be a problem for plants which need to photosynthesise to grow.

Alien carp cause turbidity by bottom-feeding and uprooting plants. This is a problem for native fish.

This image shows the junction of the Murray and Darling Rivers. The Darling River is the murky looking one on the left, while the Murray is the clearer looking river on the right.

2.a. Turbidity is caused by soil/dirt running off the land.

(Students might also mention farming, grading etc.) From the video they won’t know about carp – see notes at left).

2b. Their writing/drawing should start with aquatic plants not surviving because light is too low.

(They should refer to these plants as the food source for many creatures which are in turn food for larger fish and other aquatic life, plus waterbirds etc.)

Each student group reports back to the class what they found out. Students can show the class the animations or movies they researched, time permitting.

The following activities are suggested to embed the learning.


Several options are provided below. Some will require more time than others.

A: Classifying water quality problems


Students analyse information and categorise sources of water quality problems into a bar chart (assessment).

  • Stickers (30 per student group) of 4 different colours
  • graph paper
  • paper bags

Put an assortment of stickers into each bag and give one to each group.

Each bag represents a ‘water sample’ from a different catchment. Each sticker represents a source of water quality problems, e.g.

  • Purple = sediment
  • Red = fertilizers
  • Yellow = salt
  • Blue = carbon

Students draw a graph and label x axis with pollutant types and y-axis with the amount of pollutants. They separate and count the number of each pollutant in their sample and graph them. From this and the data in the following table, they predict the types of activities they think are occurring in their catchment, and propose solutions.



Types of pollutants and issues

Dryland agriculture

Tillage, cultivation, fertilizers, animal droppings

Nitrate, ammonia, phosphate, sediment


Timber harvesting, road construction, fire control, weed control

Sediment, pesticides, gas and oil


Land clearing, grading, more roads

Sediment, oil and gas


ATVs, boating, camping, fishing

Gas and oil, erosion, litter

Irrigated agriculture

Watering on top of water tables

Salt, fertiliser

Mining (surface)

Digging, trucks

Sediment, heavy metals, acids, nutrients

Dams and water use rules

Prevention of flooding

Carbon build-up

Urban storm runoff

Lawns and gardens, painting, chemicals down drains

Oil, gas, nutrients, pesticides, chemicals

B: Make a Secchi disc

See teacher resources below.

C: MDBA water quality monitoring

Investigate the MDBA’s River Murray water quality monitoring program

D: A novel indicator for water quality


We can easily measure a number of indicators of water quality, including dissolved oxygen content, pH, temperature, salt content and a lot more, using chemical indicators, thermometers and meters. Physical sampling is also undertaken for phytoplankton and bacteria.

However, there’s another way to tell how healthy waterbodies are—looking to see what macroinvertebrates can be found there (see teacher resources to order or view a poster).

Investigate using the Centre for Freshwater Ecosystems bug guide and MDBA’s macroinvertebrate sensitivity index poster.

E: Solutions to water quality problems


View wetlands as water filters: see the ABC's Wetlands clean up stormwater (video).

  • Research biofiltration and draw a diagram of how it works.
  • Create a biofilter (you will need test tubes, a couple of sizes of sand, gravel and ideally some charcoal. Layer the material with the most coarse on the bottom).
  • Write a short explanation of how wetlands could work as biofilters.

F: Design a catchment


Design a 3D model showing sources of water quality problems using software such as Lego digital designer or a CAD program. If technology isn’t available, this could be an annotated diagram (ACHGS049).

G: Catchment Detox


The ABC's Catchment Detox game is a fun and engaging way to look at issues of water quality (and availability).

Teacher resources

Nitrogen cycle diagram

Blackwater visual explainer

Secchi disc template

Secchi disc teacher sheet

MDBA macroinvertebrate sensitivity index poster

Catchment Detox educational game


Continue to Water security

Updated: 12 Dec 2018