Experts say action must be taken to avoid catastrophic failure at Canberra’s major water supply.

The ACT’s Auditor-General says the Lower Cotter Catchment, Canberra's primary source of drinking water, faces several risks.

Auditor-General Maxine Cooper warned in a report last year that there is an “extreme” risk of fire from fuel loads that have been piling up since bushfires in 2003.

If there were a fire followed by a major rain event, Dr Cooper warned that “the under-maintained and the damaged sediment control structures would be overwhelmed and ineffective”.

“The [catchment] is exposed to significant risks, which are interrelated and which, under adverse conditions, could accumulate and lead to a catastrophic failure of the water catchment.”

The government has been working in the past year to address all 12 recommendations made in the Auditor-General’s report, including efforts to remove invasive pine wildlings, repairing fire trails, controlling pest plants and animals, and increasing staff presence.

The Act Government has even created a new conservation agency within the Environment and Planning Directorate dedicated to the catchment.

The Legislative Assembly's standing committee on public accounts has now reported on the responses to the Auditor General’s report.

The committee's report calls on the government to “implement a sustainable funding model for management of the Lower Cotter Catchment”.

“The committee remains concerned that in the absence of a sustainable funding model... the ongoing risk profile for the catchment remains significant.”

It called for more transparency on the funds for managing the water supply, and for more frequent updates on progress.

The Legislative Assembly also wants an update on the progress of pine wildling removal trials by the end of this year.

Water quality consultant Ian Falconer calls pine wildlings a “disaster in a drink water catchment”.

He says there is no “magic cure” for removing the pines.

“It is not easy and it is not cheap, whichever way you do it,” Professor Falconer said.

“But what you cannot do is what they did last time after the fires. They windrowed all the dead sticks and rubbish into vertical windrows going up the slope, let them dry for a couple of years and then set light to them.

“They generated burnt earth growing straight up and down, which is just an erosion gully waiting to happen. It was absolutely atrocious management.”