2007/2019 – Warragamba Dam (NSW) – Algal Blooms, Sediment and Ash Concerns

Sydney’s drinking water could be polluted by bushfire ash in Warragamba Dam catchment, expert says

Large deposits of sediment and ash in reservoir which supplies 80% of the city’s drinking water creates ‘serious situation’


Sydney’s drinking water supply is at risk of the same “worst case scenario” facing some New South Wales regional communities, where large amounts of bushfire ash has been swept into dams by heavy rainfall, a water expert has warned.

Stuart Khan, a water quality security expert and environmental engineer from the University of NSW, said recent bushfires had left large deposits of ash in the Warragamba Dam catchment, which supplies 80% of the city’s drinking water.

“The situation in Sydney is really serious,” Khan said. “Having a reservoir full of soil and sediment and ash is in itself a real problem, because it makes water treatment processes more difficult.

“There will be a huge amount of ash sitting in the catchment now. The best case is we get gentle rainfall for weeks and months that allows some gentle regrowth. If we have a big storm or a big wet weather event in Sydney’s drinking water catchment, we will see some of that ash running into the dam.”

WaterNSW has said fires in the catchment areas posed no risk to water quality “at this time” and that the authority had been working to minimise potential effects.

“The potential for water quality impacts on dam storages will depend on the extent and intensity of the fires and timing of the next significant rainfall,” it said last week.

Precautionary planning was under way, and it could use sophisticated measures, including taking water from variable places or storage depths, or deploying booms and curtains to isolate flows that posed a water quality risk.

Khan said some regional communities, such as Tenterfield in the northern New England region of NSW, had already had their drinking water supply polluted by ash. Tenterfield residents have been boiling their water for more than 70 days.

When ash – which contains large amounts of organic carbon – enters the water supply it can take oxygen from the water and change the water chemistry. Khan said fish kills were possible, as was blue-green algae.

The more sediment in the water, the more difficult to treat. Khan said that while Sydney had backup systems to deal with a similar situation, the threat was much greater in many regional communities where treatment infrastructure was old or outdated.

“Across the east coast of NSW, almost all of our water supply is surface water,” he said. “The way we protect catchments is having forested areas around them. If there is a bushfire in the catchment, it affects that protection.

“We’ve got lots of places where supplies draw from a single reservoir, a single treatment plant, with relatively simple treatment in place.

“It’s time to have a good hard look at drinking water plants around NSW and ask the question: are they up to scratch on a day-to-day basis? Do they have the resilience … [to] withstand these hazardous events and continue to reliably provide safe drinking water quality?”

Patrick Lane, a forest hydrologist from Melbourne University told the ABC that steep, dry-forested areas in particular were prone to mud slides after bushfires.

“I think water authorities in the past probably thought this was something that would come along once every now and again, but I think we need to be thinking much more about this could be something that happens every few years,” Lane said.

Catchment Authority denies half Sydney’s water supply unusable


2 November 2007

he Sydney Catchment Authority has dismissed claims Sydney’s water supply is under threat from a toxic algal bloom in Warragamba Dam.

State Liberal MP Michael Richardson says Sydney Water catchment documents, obtained through a Freedom of Information request, show the algal bloom in Warragamba Dam has rendered about 500 billion litres unusable.

Mr Richardson says using water from deeper within the dam significantly reduces the drinkable supply.

“Very high levels of blue-green algal bacteria within the top 12 metres of the reservoir mean the water has to be drawn from below that point,” he said.

“Effectively, it knocks out half the water behind Warragamba Dam.”

He says none of Sydney’s filtration plants are fitted to treat algal toxins.

“There’s nothing at the Prospect water filtration plant, which treats 85 per cent of Sydney’s water, so really there’s nothing standing between us and a water shutdown – apart from luck.”

But Catchment Authority acting chief executive says Ian Tanner says the algal bloom is not toxic and only affects about 50 billion litres, or about three to four per cent of the dam’s supply.

“We’ve got good flexibility in not only the source of water but also the depth from which we can take it,” he said.

“We can go down even deeper if we wanted to because Warragamba, where we take the water from, is 85 metres deep and this algae is only in the top 10 to 12 metres.”

The New South Wales Government has also denied reports the algal bloom is threatening half of Sydney’s water supply.

NSW Water Minister Phil Koperberg says there is no imminent threat to the drinking water supply.

“Very little of the total volume of the water in Warragamba Dam or Lake Burragorang is affected,” he said.

“On current indications, we would have enough unaffected water to last Sydney for between four and six years.”

Cyanobacterial Bloom Management Current and Future OptionsAbstracts from the meeting held 12 & 13 August, 2009, Parramatta, NSW

Cyanobacteria bloom in Warragamba Dam in 2007 Bala Vigneswaran

Senior Water Quality Scientist, Sydney Catchment Authority

A cyanobacteria bloom developed in Warragamba Dam in August 2007, and persisted over three months. This paper describes the nature of the cyanobacteria bloom of 2007, the operational responses undertaken by the Sydney Catchment Authority (SCA) and the preliminary results of the analysis of relevant data.

The cell count of Microcystis exceeded 100,000 cells/mL in the first week of September 2007, and reached 700,000 cells/mL near the dam wall in October 2007. A cyanobacteria bloom of this proportion has never occurred before near the dam wall. The strength of the bloom started to decline in December 2007.

The SCA managed this event in accordance with its Bulk Raw Water Quality Incident Response Plan. A comprehensive monitoring and surveillance program was developed in consultation with Sydney Water and NSW Health. The incident management actions were continually reviewed. This effective management meant that treated water continued to meet Australian Drinking Water Guidelines (ADWG), and the consumers in Sydney were not impacted in any way.

More than 120 water samples were tested for toxins, and all but four detected no toxins. On the four occasions where toxins were detected, the toxin levels were well below the guideline values, and immediate re-sampling of the same sites detected no toxins.

A molecular technique was used to investigate the potential presence of genes in the cell population that might produce Microcystin toxin. Microcystis species detected near the dam wall had a very low fraction of cells with a capacity to produce toxin. A fluorometric probe was trialled as a means to study the distribution of cyanobacteria cells with mixed results.

Remote imagery was also analysed to investigate its potential value in the monitoring of a bloom. To better understand the nature and cause of the bloom and therefore the risk of similar events in the future, the SCA undertook a comprehensive analysis of the available data. Before the event the storage volume in the dam had declined to only 681,000 ML, i.e., 34% of the full capacity.

The subsequent inflow event in June 2007 delivered an inflow of approximately 489,000ML over a period of six weeks. Therefore the volume of water delivered represented about 72% of the volume of stored water prior to the event. This inflow raised the water level by approximately 9 metres.

It was concluded that the cyanobacteria event was the result of the unprecedented combination of the following factors; (a) a significant inflow, which entered the storage as an underflow, (b) timing of the inflow during the seasonal cooling cycle between April and July, (c) substantial levels of nutrient loading through catchment contributions and remobilisation from the bed deposits within the storage, (d) efficient transport of the nutrient rich waters to the dam wall, (d) low initial storage volume and high inflow volume to storage volume ratio, and (e) the environmental conditions conducive for a cyanobacteria bloom.

Better boil ya billy: when Australian water goes bad

July 11 2018 (by Ian Wright)


Many Australians take it for granted we can drink untreated tap water, without worrying about the health effects.

However, a recent audit criticised the regulation of pollution in the massive Warragamba Dam drinking water catchment, the biggest single metropolitan water reservoir in Australia.

The Auditor-General’s report found that the NSW Environmental Protection Agency (EPA) was not effectively regulating water pollution in drinking water catchments. The report mentioned WaterNSW, which is the authority that supplies the majority of Sydney’s water needs. The report concluded that responsible bodies like the EPA and WaterNSW need to work together more effectively to protect Sydney’s water from pollution.

Problems in the Warragamba Dam, which is surely the most regulated and monitored water supply in the country, raise the issue of regional water quality.

Sydney’s salinity is rising

The audit was triggered by an independent triennial review of Sydney’s water supply (in which I participated), which was completed last year.

One of the issues we identified was rising salinity in Warragamba Dam. Although Sydney’s water supply has relatively low salinity by Australian standards, the level in Warragamba Dam (measured as electrical conductivity) was about twice that of other, smaller storages.

Coal mines in the Warragamba catchment are a major source of salinity. The Springvale mine is the largest, and it disposes a large volume of wastewater to the catchment. I have been very concerned about the impact of this coal mine discharge on water quality for many years.

The Springvale mine’s current discharge licence permits more than 10 Olympic swimming pools of saline waste water to be released daily into the Warragamba catchment. The waste water from Springvale has a salinity level eight times higher than that of Warragamba Dam.

Regional water problems

If pollution is allowed in such an important water supply, what is happening to your local water supply?

Currently there are several water supplies in Tasmania that have “boil water” alerts. Boil water alerts indicate that harmful pathogens could be present in the water supply, and it should be boiled for at least a minute before drinking.

In some communities in Western Australia the water supply is tainted by contamination that is not managed by simply boiling it. High nitrate levels in tap water have been reported from some communities, such as Meekatharra, a small township 700km northeast of Perth that relies on groundwater.

High levels of nitrates in the water cannot be easily treated, and are particularly dangerous for infants. When drunk by babies it can affect their blood oxygen levels and cause a disease called blue baby syndrome. Western Australia’s Water Corporation recommends that babies under three months do not consume the water, and bottled water is recommended for young babies.

Water in Katherine, in the Northern Territory, has been contaminated by toxic and persistent chemicals used in firefighting foam. The toxins have accumulated in the groundwater. Many other communities across Australia have also been similarly affected.

Uranium has also been reported in some remote community water supplies from the Northern Territory. Alarmingly, uranium levels were above Australian drinking water guidelines, and there are no clear guidelines for managing the problem.

These examples from regional communities reinforce the importance of preventing contamination from entering water supplies.

It is worth remembering that 20 years ago protozoan pathogens from the Warragamba supply resulted in several boil water alerts across Sydney.

The NSW Auditor-General’s report found serious issues in how the EPA manages water pollution in Sydney’s drinking water catchments. For example, much of the data used by the EPA was self-reported by industry sources.

It may be surprising to many Australians that our water quality varies so wildly across the country. Our pollution watchdogs need to be strengthened and resourced properly so they can protect our most fundamental resource.