The man was found stuck in his car in Paddy's river below the Cotter dam on Sunday evening around 5pm. Emergency personnel were assisting him when his vehicle was flipped by the floodwaters and swept away.

His body was found a short time later on an island in the middle of the river, but it was deemed too dangerous to immediately retrieve with waters raging.

"It's an absolute tragedy and our condolences go out to the family," Officer in Charge, Station Sergeant Harry Hains said.

It is not known how long the man had been stuck in the river before rescuers arrived on Sunday, with mobile service in the area next to none.

"I'm sure you can imagine if you were stuck in a floodwater it would be a fairly distressing thing," Sergeant Hains said.

"The floodwaters yesterday ... were extremely strong, savage, with a lot of debris, large logs coming down the river. The force was enough to flip a two-tonne ute."

Police were called to the Cotter dam area after a report of two teenagers stuck in a four-wheel-drive, unable to cross the river. Those 17-year-olds were safely rescued by authorities who then found the 37-year-old man stuck in his car.

Another two men died in floodwaters in Bowral and Leppington in Sydney's south-west prompting a desperate plea from authorities to avoid rivers and creeks at all cost.

Conrad Barr, chief officer of the ACT State Emergency Service, said the Cotter incident was "far and away most serious and regrettable incident we've had to attend over the weekend."

"Any flood-related death is something we don't want to deal with. It's far safer and better not to try to drive through floodwater than to impose the risks associated with a tricky rescue on our dedicated professionals in all of the emergency services."

"All our services dedicated people find these sorts of things difficult and potentially traumatic."

Mr Barr stressed that no one should attempt to drive through floodwaters.

"You can imagine the situation that's been described with raging water and a vehicle stuck and crews trying to do their best to get to that person ... it's a very disappointing thing for anybody who's in that circumstance."

The reasons why he was in the middle of the river will subject to a full police investigation and coronial review.

Muddy brown water billowed through the smashed windscreen of the submerged ute as emergency crews continued to try to extract the vehicle from the swollen river on Monday morning, police and emergency services having earlier retrieved the Kambah man's body.

The floodwaters were caused by an intense weather system on the NSW coast that brought heavy rain to much of south-eastern Australia.

Canberra received a month's worth of rain in a day over the weekend, but escaped the worst of the wild weather that lashed the NSW south coast.The ACT was drenched with 48.8 millimetres of rain between 9am and 5pm on Sunday, which was more rain in a day than the June average of 42.9 millimetres.

The rain continued throughout the night, with Canberra Airport recording 64.6 millimetres from 9am on Sunday to 8am on Monday, and 78.4 millimetres at Tuggeranong.

The deluge even led to rising waters in Lake George, the million-year-old lake north of Canberra than has been empty for several years.

While the worst of the rain passed on Monday morning, light showers remain a possibility across the territory in coming days.

The Bureau of Meteorology expect up to 8 millimetres of rainfall by the end of the week with most of it likely to fall on Thursday afternoon.

Temperature are forecast to keep temperatures around 13 degrees with cloud cover keeping overnight temperatures above freezing until next week.