Ash from raging bushfires could contaminate Sydney's drinking water with blazes closing in on a dam that holds 80 per cent of the city's supply.
Two giant fires are burning on the north western edge of Lake Burragorang, west of Campbelltown, where the Warragamba Dam is located.
The massive blazes are expected to combine and the Rural Fire Services fear they could spread across the lake to the east.
University of NSW professor Stuart Khan, who has studied the threat of bushfires to water supplies, told Daily Mail Australia that this event would pose 'some serious water quality risks'.
He said if the fires are followed by a large rain fall event, the sediment from the ground will wash into Warragamba Dam.
Smoke erupting above Green Wattle Creek where Rural Fire Services are battling an out-of-control blaze threatening to contaminate Sydney's water
The ash, which is comprised of organic carbon and phosphorous, can cause chemical reactions to occur in the water which can produce toxins.
'These can lead to serious water quality impacts including deoxygenation and the growth of cyanobacteria and algae,' professor Khan said.
'These organisms can produce toxic chemicals or change the taste and odour of water.
Deoxygenation can also make other chemicals more soluble in water, such as iron and manganese- which can turn water orange or red.
Warragamba Dam (pictured) is at risk of contamination from bushfire ash which could cause discolouration and taste changes which could last months
He said given summer rainfall levels the risk of an algal bloom was high.
Based on previous incidents, he said, if infected, the altered water conditions and off-taste could last months.
Their is currently no fire risk to the treatment plant and its major infrastructure.
A WaterNSW spokesman said while water quality is yet to be compromised, they are confident they would be able manage the risk to public health.
'Fires burning in Sydney's