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Severe infestations of blue-green algae in Sydney’s drinking water catchments have soared 800 per cent, according to an audit which warned climate change is putting the sensitive waterways under increasing threat from toxic blooms.


Warragamba Dam
Warragamba Dam, the main source of Sydney's drinking water supply. JENNY EVANS

The audit also called for an investigation into levels of pollution in Coxs River, which feeds into Warragamba Dam, Sydney’s main drinking water reservoir.

There are no government water quality monitoring stations in the section of the upper Coxs River that is of most concern due to a cluster of polluting businesses nearby.

A Sydney Water spokesperson said there was no risk to consumers because water is treated to meet Australian Drinking Water Guidelines.                                                                                                    

However Professor Stuart Khan from the University of NSW said the same guidelines stress that protecting the catchment is a key pillar of providing safe drinking water.

“If we had to treat poor quality water, it would require us to use more energy and more chemicals,” he said. “Costs to treat drinking water would increase, as would the greenhouse footprint and other environmental impacts.”

The Sun-Herald can also reveal there are health concerns over the potential use of blue-green algae tainted water to grow crops in the Sydney basin.

The audit of Sydney Drinking Water Catchment was released last month, covering 2016 to 2019.

It was prepared by independent consultants for WaterNSW, the agency in charge of protecting the health of the catchments.

A WaterNSW spokesman said it would review the audit and report back to the government but welcomed a finding its management of the catchment had “substantially improved” in recent decades.

The audit highlighted the continued risk of mining in the catchment after three oil spills had to be quickly remediated before they posed a threat to consumers.

Further investigation was also needed into the rehabilitation of coal mines and the water losses and water quality impacts they caused, the audit found.

“This audit provides strong evidence of the ongoing impacts and risks associated with mining,” Professor Khan said.

The WaterNSW spokesman said the government had recently adopted the recommendations of the Independent Expert Panel for Mining in the Catchment which “should address public concerns”.

The audit found the catchment was coming under increasing pressure due to climate change, which increased the likelihood of bushfires and blue-green algae blooms.

There were 223 “red alerts” for severe blue-green algae outbreaks between 2016 and 2019, up from 23 in the previous audit period.

The overall number of alerts was 1266, more than double the 556 in the previous audit.

Some strains of the algae are harmless but others produce hazardous toxins that can cause vomiting, liver and nerve damage, liver cancer and even death in humans and animals.

Of growing concern to scientists is also a potential connection between a toxin sometimes found in blue-green algae and motor neuron disease.

Dr Darren Baldwin, a Charles Sturt University professor who advises the government on extreme water quality events, said that warm and dry conditions associated with climate change “certainly” increased the likelihood of blooms.

“When algal blooms occur, councils have to invest significant additional money in water treatment,” he said.

A research student at the University of Sydney uncovered toxic blue-green algae in waterways used to irrigate crops in the Hawkesbury-Nepean catchment in 2018.

Kansas Keeton, who has now relocated to the United States, called for further investigation into how the algae was affecting the crops, amid “extensive” scientific evidence the dangerous toxins can accumulate in vegetables such as tomatoes, lettuce and carrots.

A WaterNSW spokesman said its comprehensive water quality monitoring program could detect blue-green algae, and respond with operational changes to avoid sourcing affected water.

It could be effectively treated with powdered activated carbon and chlorination, he said.

The spokesman added while climate change could pose a risk to long term water security, WaterNSW was working to develop "viable mitigation options".

The audit called for an investigation into pollution in the upper Coxs River and Wingecarribee Rivers due to “ the relatively high numbers of sites of pollution and contamination”.

The Coxs River is the second-largest source of water for Warragamba Dam, while the Wingecarribee River tops up Sydney’s supply when reserves become low.

WaterNSW’s only monitoring station in the upper Coxs River is located away and upstream from pollutant sources, the audit found, including explosives production, sewage plants, a power station and the Springvale Mine coal mine.

A court blocked the mine’s extension in 2017 because of concerns about its effect on the catchment, but the NSW government overturned the decision.

The WaterNSW spokesman said it would conduct an investigation into programs aimed at preventing and minimising pollution in the locations flagged in the audit.

“Where there are opportunities for improvement WaterNSW will pursue these with relevant stakeholders,” he said.

The spokesman added that there were a series of monitoring stations in the upper Coxs River operated by businesses as part of their EPA license conditions, which provided "extensive information". However WaterNSW's monitoring regime would also be reviewed.


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