After a brief reprieve, a second wave of rain hit the region yesterday bringing more than 35mm which destroyed and covered bike paths, bridges and roads across the region. A further 50mm was expected today by the ACT State Emergency Service while the Bureau of Meteorology predicted a slightly more conservative 15mm to 35 mm.

A severe flash flooding warning remains for the ACT while several roads were closed last night, including one lane of Canberra's main street, Northbourne Avenue. Queabeyan police and SES crews were last night called to a rescue at Araluen Creek, where at the time of printing one person was reportedly stuck in a tree while another was swept downstream.

Across the region Cooma businesses sandbagged their premises and 600 residents evacuated the town in case of flooding while north of Canberra an evacuation alert was lifted in Goulburn.

As of last night the ACT State Emergency Service had received a total of 760 calls for help since the wet weather started 3pm Tuesday.

Around 3500 people across NSW face an indefinite wait before they can return to their homes as continuous heavy rain swells rivers across the state.

Almost 2000 people in Sydney's flood-threatened north-western fringes were told to evacuate yesterday as relentless rain put pressure on the already swamped Hawkesbury-Nepean River.

Millions of litres of water continued to spill over the Cotter Dam's new wall yesterday, a spectacle that has attracted hundreds of onlookers.

At its peak on Thursday, 29,000 megalitres was flowing into the dam and that had slowed to about 6000 megalitres yesterday.

"But it's expected to increase again with the rain we've had in the afternoon," an Actew Corporation spokesman said. The spokesman said millions of dollars of machinery left behind at the flooded site had not been washed away as of yesterday afternoon.

But water still surrounded the equipment and a certain amount of damage, still impossible to assess at the moment, was guaranteed.

Rain was pushing 5000 megalitres of water a day over the spillway at Googong dam, but the figure paled in comparison to the 98,000 megalitres of water a day that thundered over the dam wall during floods in 2010.

While flow rates were not available for Corin or Bendora dams, water levels at both were at 100 per cent.

Recreational areas and walking trails around the four dams have been closed and the Cotter River Bridge is closed to vehicles.

Mugga Lane between Long Gully Road and the Monaro Highway was also closed last night and warning signs were in place.