Cataract Dam, above the escarpment from Wollongong, has fallen to just 27.1 per cent of its capacity and has been taken offline for drinking water.
Subscribe now for unlimited access.
$0/
(min cost $0)
or signup to continue reading
The dam's water level has fallen 1.5 percentage points since last week, and has dropped from a level of 29.1 per cent in three weeks.
It's a massive drop from its average level for 2018, which was 43.1 per cent, and its levels from the previous two years, which were both above 87 per cent.
Cataract is currently offline with supply ... being provided from Nepean Dam, which in turn is receiving water transfers from the Shoalhaven
- WaterNSW
Three weeks ago, when Cataract was at 29 per cent, a WaterNSW spokesman said this was a similar level to that during previous droughts.
"Cataract Dam currently sits at 29 per cent of capacity, a level it reached during drought periods at the start of the 2000s and again midway through that decade," he said.
"Cataract is currently offline with supply to Macarthur water filtration plant and the Upper Canal being provided from Nepean Dam, which in turn is receiving water transfers from the Shoalhaven."
It has since dropped further to 27.1 per cent, which represents 26,220 megalitres, from a capacity of 97,190ML.
The Mercury asked WaterNSW what had happened since 2017 to cause the water level to sink from an average of 87.5 (2017) to 43.1 per cent
"WaterNSW has used Cataract Dam more than other Upper Nepean storages recently to allow for essential maintenance and upgrade works at Pheasants Nest weir," the spokesman said.
"Greater Sydney' dam storage network is configured in such a way that supply can be adjusted to distribute demand between Upper Nepean storages, and to allow for important maintenance work to ensure the network is operating at full capacity."
Supply to the Macarthur plant can be sourced from any of the four Upper Nepean storages: Cataract, Cordeaux, Avon and Nepean.
These dams are running low as well, with Cordeaux at 41 per cent of storage capacity, Avon at 49 per cent, and Nepean at 41 per cent.