The water quality of the Cooks River is an area that many of our members and broader community are keenly interested in. The history of the river goes from a pristine native waterway and habitat (200 years ago) to a highly degraded and polluted urban drain.
Recent EPA Microplastics report on NSW rivers.
The Mudcrabs have been involved in many of the initiatives aimed at dramatically improving the water quality. Amongst these have been:
– Monthly working bees to gather and remove litter from the waterway.
– Re-establishment of native plants & bushland across the 15 bushcare sites that are on both sides of the river.
– Advocacy for better quality water through litter collection booms/traps, support of anti-pollution initiatives e.g. single use plastic bag bans and recycling schemes.
Recenty we have been in discussion with Sydney Landcare on restablishing a water quality testing regime to assess the current state of the Cooks River and be able to identify key threats to water quality and how to take action.
We have worked with Sydney Landcare on delivering workshops to the Mudcrabs volunteers and are now initiating a program of water testing to help develop a better understanding of the issues relating to overall water quality. The Mudcrabs are fortunate to have a number of willing scientists in our ranks as well as keen citizen scientists in the community to help out with the data collection and management of the program.
Watch this space for further updates on our findings.
If you are interested in further details please contact : info@mudcrabs.net.au
Cooks River Catchment Map
The Cooks River catchment covers over 100 square kilometres and spans Georges River, Strathfield, Canterbury, Inner West and Bayside Council areas.
The Cooks River itself is 23 kilometres long but when the various tributaries are included the main stream is over 60 kilometres. The upper edge of the catchment extends from Rookwood Cemetery to Redfern, the southern edge runs from Hurstville through Beverly Hills/Roselands to Strathfield.
This means that every gutter and stormwater drain in the catchment flows directly into the Cooks River and on to Botany Bay. So a drink bottle or snack wrapper packet dropped in Rookwood Cemetery will make its way to Botany Bay via the gutters and drains of the catchment. Likewise, any overflow or industrial waste that gets into the gutters or stormwater system will flow directly into the Cooks River then Botany Bay.
List of Potential Mudcrabs Testing Sites:
Here is a list of active Mudcrabs working-bee sites – the bold one are currently having regular water testing done by Mudcrabs volunteers.
Tempe Saltmarsh – Gough Whitlam Park
Thornley Street – Children’s Garden
Marrickville Golf Course – Wave Rock
Southbank – Earlwood
Foord Avenue – Hurlstone Park
Ewen Park – Hurlstone Park
Boat Harbour – Hurlstone Park
Sugar Mill – Hurlstone Park
Cup & Saucer Creek Wetlands
Wave Rock – river clean-up site
Close Street – river clean-up site
Racecourse – river clean-up site
Rosedale Reserve – Bushcare
Tasker Park – Canterbury
What is being tested
The Mudcrabs are working with the Sydney Landcare Streamwatch program to monitor and record information on the water quality of the catchment. We are measuring these water health indicators. As more data is gathered we can build up a more complete water health picture as well as inform the relevant Local Council of any alarming indicatiors.
Streamwatch Testing Kit
The Streamwatch program (coordinated by the Greater Sydney Landcare Network) primarily utilizes two main types of water quality kits. We are currently using the ALERT Kit – designed to be a quick, “grab-and-go” test kit. It provides accurate data without the use of concerning chemicals.
What the Kits Measure
Using the Streamwatch kits, volunteers perform simple tests to measure:
- Temperature
- Dissolved Oxygen
- pH levels
- Electrical Conductivity(salinity)
- Available Phosphates
- Turbidity
All data is entered into the Atlas of Living Australia and can be viewed by looking at the Cooks River Streamwatch data.
What the water quality measurements tell us about the state of the water in the Cooks River system – Key Indicators and Their Significance
Temperature:
What it measures: The temperature of the water, typically in degrees Celsius
Significance: Temperature directly affects the metabolic rates of aquatic organisms and how much oxygen can dissolve in the water. Sudden or unnatural changes can stress fish and macroinvertebrates, often caused by the removal of shading vegetation or thermal industrial runoff.
Dissolved Oxygen (DO):
What it measures: The amount of oxygen gas ((O_{2})) dissolved in the water, usually measured in milligrams per Litre ((mg/L)).
Significance: Aquatic animals—from fish to waterbugs—rely on dissolved oxygen to breathe. Levels can plummet when excess organic matter (like sewage or plant material) decomposes in the water. Consistently low DO causes “hypoxia,” which can lead to fish kills.
pH (Acidity and Alkalinity):
What it measures: The concentration of hydrogen ions, indicating how acidic or alkaline the water is.
Significance: Most aquatic organisms thrive in a pH range of (6.5) to (8.5). Levels that are too high or too low can disrupt fish gill functions, prevent the reproduction of aquatic life, and cause heavy metals in the sediment to dissolve and become toxic.
Electrical Conductivity (EC):
What it measures: The ability of the water to conduct an electrical current, which acts as a proxy for dissolved salts (salinity).
Significance: Freshwater naturally has a low EC. Spikes in conductivity suggest unnatural inputs like sewage leaks, urban runoff, or rising groundwater, which can dehydrate or poison sensitive freshwater plants and animals.
Nutrients (Nitrates and Phosphates):
What it measures: The levels of nitrogen and phosphorus compounds in the water.
Significance: While essential for plant growth, excessive nutrients (from agricultural fertilizers, detergents, and sewage) cause eutrophication. This leads to rapid, out-of-control algal blooms, which eventually die, decay, and deplete oxygen levels to dangerous lows.
Turbidity:
What it measures: The cloudiness or haziness of the water caused by suspended particles (like sediment or algae).
Significance: High turbidity blocks sunlight, preventing aquatic plants from photosynthesizing, and can clog the gills of fish. It is typically caused by soil erosion, construction run-off, or severe algal blooms.
Specific Threats to the Quality of the Cooks River
1. Raw sewage overflows(after heavy rain events).
2. Industrial run-off
Poor waste mitigation which allows liquid and semi-liquid pollution to flow via gutters and outfalls directly into the Cooks River. (Link to recent pollution fines)
3. Domestic run-off
Litter/waste/stormwater runoff via catchment gutters feeding directly into the Cooks River system. Mudcrabs river clean-up activities (monthly) regularly collect 20 to 40 bags of plastic bottles, food packaging and micro-plastics.
4. Algal Blooms
These blooms eat up lots of Oxygen, cloud up the water reducing light & releasing toxins – all very harmful for marine life.
5. Speeding watercraft – illegal activity
Powered watercraft (inc. jetskis) travelling at excessive speed stir up the heavy metals (and other pollutants) stored in the river bed and release them into the main stream that flows into Botany Bay.