Googong Dam is full after a week's deluge dumped about 2 gigalitres of water into the catchment.

According to forecasting website Weatherzone, owned by Fairfax Media, publisher of The Canberra Times, more than 90 millimetres of rain has fallen on the ACT for September - nearly twice the monthly average. The territory's dam storage levels have received a 4 per cent boost since the weekend.

Canberra's combined storage volumes sit at 73 per cent capacity, with Bendora Dam nearing 100 per cent, and the new Cotter Dam rising to about 27 per cent.

ACTEW Water said Googong Dam would continue to spill water while at full capacity.

"As a water storage facility, this is welcome news as we progress further into spring and summer."

On Thursday, visitors watched as water poured over the spillway at Googong Dam.

Spectator David Dawes said it was excellent to see the dam at full capacity.

"It's great out here; it's fantastic," he said. "They've virtually secured the water for the future."

Another bystander, Susan Hengst, who was visiting from Brisbane, said it was "surprising" to see the amount of water in Googong Dam.

A former Queanbeyan resident, Ms Hengst said she remembered Queanbeyan's significant 1974 floods. "Our backyard was on the river," she said. "We have four steps at the back and it came up two."

On Wednesday, a minor flood warning was lifted for the Queanbeyan and Molonglo Rivers.

The rain is expected to increase again on Friday, with possible showers in the morning and afternoon and a top of 16 degrees. On Saturday the showers are expected to ease with a high of 19 degrees.