Everyone who uses Lake Burley Griffin water for irrigation faces having the taps turned off by the start of March.
D-day was originally expected to be last Wednesday, but Canberra's freak hailstorm has given a raft of government agencies a temporary reprieve.
With temperatures soaring and the lake level already 510 millimetres below its normal level, it's just a matter of time before high-level water restrictions are introduced.
That happens when the level drops to 600mm, which could see all irrigators forced to buy potable water instead.
The ACT government, the National Capital Authority, the National Botanic Gardens, the Governor-General and Royal Canberra Golf Club head a list of irrigators who rely on lake water for their watering.
The NCA originally forecast last Wednesday as the day the 600mm mark would be reached.
But the hailstorm saw the lake level jump 25 millimetres and the NCA said they were no longer able to accurately predict a new cut-off date.
Unfortunately, the lake has dropped back to 510mm over the past nine days.
If that rate of decrease continues, it would see the 600mm mark reached on March 2.
That's without factoring in the oppressive heat forecast for the next few days.
Or any rain. Although that is looking rare over that time frame.
When it does fall to the dreaded 600mm mark, government regulations state lake water can't be used for irrigation.
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The lake's current level falls in the medium range, which means irrigators will have their allocations cut to below total inflows.
The Captain Cook Memorial Jet has already been turned off until further notice due to the low level.
"The rate at which the lake level is falling is highly dependent on the weather and abstraction so it is very hard to estimate with any certainty," an NCA spokesperson said.
High-level restrictions mean no water can be taken from the lake.
But the government said there was some discretion in making that call.
"There is flexibility in the guidelines that advise that, 'Restrictions on water abstraction can occur if the lake level drops', and the type of restrictions that may be applied," an ACT government spokesperson said.
"The [Environment Protection Authority] works with the NCA to determine water abstraction targets that have the least impact on abstracters while maintaining lake levels to the satisfaction of the NCA.
"The restrictions vary because not all abstracters have water demand at the same time.
"For instance, Floriade's maximum water demand period lasts for a few weeks each year and rural irrigators in Pialligo have periods of limited water use.
"Lake levels can also change in a very short timeframe, which affects the need and size of restrictions."
But the NCA told The Canberra Times it would take a significant amount of rain over an extended period to reverse the current trend.
With the lake level now in the medium range (400-600mm), irrigators have been given volumetric limits for January 28-February 28.
Those limits are designed to be less than the total inflow to the lake.
"Medium level restrictions have been introduced, based on a decision by the National Capital Authority," an ACT government spokesperson said.
"Licence holders were notified by the Environment Protect Authority on Friday, January 24, and were each given a volumetric limit for the period January 28-February 28."
Irrigators that use lake water are made up of a host of nurseries, including Yarralumla Nursery, Canturf Farms, and ACT government agencies the Suburban Land Agency, Events ACT, and Transport Canberra and City Services.
"The National Capital Authority advised the Environment Protection Authority on December 9 that lake levels had dropped to the point where low-level restrictions should be considered," an ACT government spokesperson said.
"Directions advising of restrictions were given to licence holders on December 16.
"Adjustments to the restrictions are currently under consideration.
"If the lake level drops more than 600mm ... lake abstraction ceases."
LIST OF LAKE IRRIGATORS: Willow Park Nursery, Beltana Grange Orchard, Pialligo Apples, Yarralumla Nursery, Flamen Nominees Pty Ltd, Canturf Farms, Hazelbrook Nursery, Land Development Agency, TCCS parks, TCCS tree watering, Pialligo Fresh Operations Pty Ltd, National Botanic Gardens, National Capital Authority, Governor-General, Events ACT, Royal Canberra Golf Club Ltd, River Road Nursery Pty Ltd.
