Canberra's 101-year-old original Cotter Dam will disappear beneath the water forever this week following the closure of the 3.4 metre high river diversion construction gate that has channelled the Cotter River around the new dam site until now.
"Closing the gate allows the mighty [new] dam wall to start doing its job, storing raw water to protect the Canberra community from the threat of severe and prolonged water restrictions such as those that have affected our city for much of the last decade," an ACTEW Water spokesman said.
ACTEW Water general manager Mark Sullivan said the old dam, built in 1912 and enlarged in 1950, could be gone in the next few days and certainly before the end of the week.
It will be the second time the 30 metre dam has been submerged in just over a year following freak weather on March 1, 2012.
This time the inundation is deliberate and permanent.
Given the enlarged dam is Canberra's water storage of last resort, the city will be in dire straits if the water level ever drops low enough to expose the old structure, located about 100 metres upstream from the new dam, in future.