Heavy rain pushes Sydney's Warragamba Dam close to the brim

Water is being released from Sydney's Warragamba Dam which is almost full to bursting after weeks of heavy rains.

The dam - Sydney's main water source - is now at 97.7 percent capacity, having surged 1.1 percent in the past week and almost two percent in the last month.

In the grip of one of the worst droughts in decades, the dam hit a low of 42 per cent in February last year, before almost doubling its capacity in the next six months.

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WaterNSW started making small, controlled releases of water yesterday at Warragamba Dam.

It's expected 3500 megalitres will be released each day for the next two weeks, Water NSW spokesperson Tony Webber said.

"The releases will take it down to slightly over 96 percent of capacity, or one metre below full supply level," he said.

Dam levels are generally kept at one metre below full capacity at Warragamba Dam in order to stop its automatic gates from being triggered.

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The Bureau of Meteorology is forecasting between three to 13 mm of rain for the Sydney region in the next week.

Under the current forecast, the dam was not expected to spill over, Mr Webber said.

Meanwhile, total storage levels across all Greater Sydney dams is at 94.6 percent. Tallowa Dam is spilling over, while Prospect Dam is at 95.1 percent.

The La Nina effect, which is characterised by increased rainfall, has led the state's remarkable recovery from drought.

According to the NSW Department of Primary Industries, just 1.4 percent of the state is now drought affected.