Dam levels across Sydney are more than double what they were six months ago and Warragamba Dam is almost at capacity after heavy downpours.
WaterNSW data on Wednesday showed Warragamba Dam at 97.7 per cent capacity after about 90mm of rain fell in the catchment area over the past seven days.
That's an increase of 11.6 percentage points since the downpours started on Friday.
This compares to one year ago when Warragamba's storage level was at 51.5 per cent capacity and in early February when it dropped to 42.7 per cent.
WaterNSW says although the dam is almost at capacity, it is not expected to spill as a result of the recent rains.
The water authority will be making small operational releases from the dam's spillway gates in anticipation of further rainfall, a spokesman told AAP in a statement on Wednesday.
The heavy downpours in the past week, which were caused by a low-pressure system, filled up Sydney's combined water storage to 96.5 per cent - up 11 percentage points since Friday.
WaterNSW says this compares to February 7 when the total storage was at 41.8 per cent capacity prior to a big rain event later that month.
Nepean Dam in Bargo and Tallowa Dam in the Shoalhaven are both spilling with more than 200mm of rain falling in the Shoalhaven catchment in the past week.
The heavy rain battered the south coast with the NSW State Emergency Service on Sunday issuing three evacuation orders for residents in flood-hit Moruya, Sussex Inlet and Nowra.
The SES said the Shoalhaven River at Nowra peaked at 4.13 metres on Monday - its highest level since 1991.
Australian Associated Press