The military and civilian emergency services have joined forces to set up a system of blocks to keep debris from being washed into the Corin dam which feeds Canberra's water supply.
In an urgent operation to beat the rain, 36 long blocks known as "coir logs" were ferried by military helicopter to the six creeks which supply the Corin dam.
The aim was to slow the flow of water when and if heavy rain happens this coming week. If the water can be slowed, sediment drops to the floor rather than being swept into the source of Canberra's water.
Fire broke into the ACT rainfall catchment area and the fear was that slurry and debris would overwhelm creeks feeding dams.
On Friday, troops put the barriers down, guided by ACT Parks and Conservation people with knowledge of local terrain. The "logs" were taken to Namadgi Visitor Centre on trucks and then taken by air to the creeks.
The operation started at first light and lasted all day, according to Neil Cooper, Incident Controller in the overall operation to control the current fire ravaging the southern ACT. His brief includes organising efforts to mitigate after-effects - like slurry from burnt ground and foliage getting into the dams.
"There's no way we could have done this with our own resources," The Incident Controller said. "The help of the Australian Defence Force has prevented a whole lot of sediment getting into the Corin dam."
He thought that the ACT government would call on the ADF again "if we are in the same situation next year and the year after".
Fears were raised because the 2003 Canberra fires worsened water quality as well as lowering the quantity of water reaching the dams.
Fires meant the land didn't absorb water so rain and debris cascaded into the dams. On top of that, when vegetation grew back it gulped up the rain which otherwise would have gone into the city water supply.
"Intense, local thunderstorms following the fires moved large sediment loads from steep, denuded slopes into the supply reservoirs, Corin, Bendora and Cotter dams," according to Professor Ian White of the ANU.
The ACT government and the Australian Defence Force has not worked together in a situation like the current fire before.
Mr Cooper said the relationship was good. It wasn't just about boots on the ground and big machines but catering, engineering and a host of other services like putting up Queensland firefighters at the Australian Defence Force Academy.
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"Our role is to provide the tasking but they've got the people and the structure to go and do it." Mr Cooper said. "We define the task, hand it to the officer and they come and see us when it's finished."
There have been glitches like when a military helicopter actually started the fire which then spread across the southern parts of the ACT. Mr Cooper said that any machine like a grader or a digger could have done the same, so dry were the conditions.
